The Effectiveness of the Life Skills Program IPSY for the Prevention of
Adolescent Tobacco Use: Mediating Processes in the Area of Competencies
Relevant within Peer Interactions
Karina Weichold
Friedrich Schiller University of Jena, Germany
Martin J. Tomasik
University of Zurich, Switzerland
Rainer K. Silbereisen
Friedrich Schiller University of Jena, Germany
This study investigated the effectiveness of a Life Skills program with regard to tobacco use
in early adolescence. The focus was on the mediating role of competencies relevant for
successful interactions in the peer context (i.e., stability against groups, self-confidence,
yielding to peer pressure), based on the expectation that peer influences represent a major risk
factor for adolescent smoking behavior. The universal school-based Life Skills program IPSY
(Information + Psychosocial Competence = Protection) aiming at combating adolescent
tobacco and alcohol use was implemented and evaluated over four years (longitudinal quasiexperimental design with treatment and control group, and five measurement points; N =
2,464 students who participated in at least one of the five measurement occasions, age 10 at
T1). Applying a growth curve modeling approach, results showed that participation in IPSY
predicted a slower increase in tobacco use over time, suggesting a weak but significant
intervention effect, compared to the control group. Moreover, increase in self-confidence and
lower yielding to peer-pressure induced by IPSY mediated the program effects on tobacco use
over time. Thus, program components focusing on these attributes seem to be particularly
effective for the prevention of youth smoking by the IPSY program.
Introduction
The consumption of psychoactive substances such as tobacco is a widespread risk behavior
during adolescence in many Western countries. In Germany, 32% of 12- to 17-year-olds
report having smoked at least once in their life, and 6% of them consume cigarettes on a daily
basis (BZgA, 2011). Because of negative health and adjustment outcomes associated with
adolescent tobacco use during early and mid adolescence (Mathers, Toumbourou, Catalano,
Williams, & Patton, 2006), effective preventive efforts against the initiation and age-typical
increase in cigarette smoking during adolescence are urgently needed. Numerous prevention
programs have attempted to influence the consumption of tobacco in young people by
lowering the impact of risk factors and increasing the influence of protective factors.
Additionally, prevention programs have aimed at supporting adolescents to learn skills needed
to resolve developmental tasks appropriate to their age, such as gaining a high peer status or
establishing first romantic relationships (see for summary Weichold, Bühler, & Silbereisen,
2008). This approach has been used particularly in universal prevention programs, designed to
be implemented before adolescents begin to smoke and developed for unselected population
groups, such as school classes.
Among the various intervention programs, school-based Life Skills programs were the most
effective ones to delay onset and to reduce the age-typical increases in frequency and amount
of cigarette smoking, both short- and long-term (e.g., World Health Organization [WHO],
2002; Tobler et al., 2000). Life Skills programs focus on the promotion of general
competences in the interpersonal (e.g., assertiveness, positive social relationships) and
intrapersonal (e.g., critical thinking, self-esteem) domains. In addition, substance-specific
skills and knowledge are conveyed (WHO, 1997). All this is supposed to support the
resolution of every-day challenges adolescents have to face while striving for the solution of
their age-related developmental tasks, such as establishing a status among their peers, and to
reduce the likelihood of substance use as a pseudo-mature behavior (e.g., smoking to behave
adult-like such as offering a cigarette to get in touch with someone) or a coping strategy (e.g.,
if adolescents fail to solve their developmental tasks; Weichold, Bühler, & Silbereisen, 2008).
Based on the existing literature, however, it is still unclear by which specific mechanisms
these programs are effective in the prevention of early tobacco use or, in other words, what
mediating processes may explain positive program effects. Research on mediating
mechanisms is important, because the identification of mediators is crucial for learning which
components of prevention programs are effective in causing changes in substance use
behaviors. Thereby existing programs can be optimized (MacKinnon, Taborga, & MorganLopez, 2002), and knowledge of the etiology of problem behaviors is cumulated. If the
modification of a risk or protective factor via a quasi-experimental intervention program leads
to a reduced increase in substance use over time then this factor is indeed meaningful in its
influence and is a true causal agent. In addition, because changes in risk or protective factors
usually precede the onset of problem behaviors, confidence about the direction of the effect
increases. Finally, the design of evaluation studies including the comparison of a treatment vs.
control group, both of which are equivalent before the intervention, provides strong evidence
that the mediation effect is not caused by exogenous factors other than the intervention
program (Howe, Reiss, & Yuh, 2002).
Various theories and descriptions of associated risk factors try to explain adolescent tobacco
use (see MacKinnon et al., 2002), thereby stressing the importance of peer influences on
adolescent smoking behavior (Chassin, Presson, & Sherman, 1990; Kobus, 2003; Pandina,
Johnson, & White, 2010). According to the Social Learning Theory (Akers, 1998), for
instance, social processes (e.g., imitation within the peer group) and cognitive aspects (e.g.,
positive attitudes towards cigarette smoking) are important to initiate and maintain smoking.
Behavior is learned by the observation of others, whereby peers (with frequent and close
contact to the adolescent) as well as parents represent the most important role models. Once
smoking is initiated, rewards such as physiological reactions or successful social interactions
modify perceptions on smoking, and promote progress to more frequent and sustained
consumption patterns. The Primary Socialization Theory (Oetting, Deffenbacher, &
Donnermeyer, 1998) considers individual characteristics (e.g., personality, skills, self-esteem)
and bonds to normative contexts, such as family or school, as antecedents of the self-selection
into peer groups that show deviant behaviors such as smoking. Spending time with deviant
peers, in turn, increases the likelihood to take over their norms and behavior styles in terms of
socialization. Empirical studies support these theories by demonstrating peer variables as
robust risk factors to explain adolescent smoking, for instance with regard to friendship
homophily where selection and socialization processes can be observed (for summary Kobus,
2003). In particular for initiation of smoking during early and mid adolescence, peer smoking
models and influences seem to be of major importance. Once smoking had occurred,
adolescents increase their number of smoking friends (Chassin et al., 1990). In addition,
studies focusing on peer-pressure and its role in the development of smoking imply that in a
deviant peer context smoking becomes normative, and pressure to smoke is more subtle,
rather than overt (e.g., smoking to be liked by others, to avoid social exclusion, to gain
approval, or to facilitate social interactions; Nichter, Nichter, Vuckovic, Quintero, &
Ritenbaugh,, 1997). In such situations, competencies and interpersonal skills, such as selfconfidence and assertiveness, are important for adolescents to resist to peer-influences and
peer-pressure (Epstein, Griffin, & Botvin, 2000). Consequently, from a prevention perspective
it seems particularly promising to target peer-related variables in order to prevent tobacco use
in youth.
Several prevention programs have indeed focused on the modification of risk and protective
factors in the peer context (i.e., peer-influences or skills relevant to effectively interact with
peers, refusal skills; see for summary Chassin et al., 1990). Among these, in particular
programs based on the Social Influence and Life Skills approach, and especially those using
interactive teaching methods such as role play or group discussions were effective, probably
because they conveyed and practiced such skills as how to resist to passive or overt social
pressure or role modeling in the peer context, or promoted enhanced positive self-perceptions
(e.g., Lantz et al., 2000; Tobler et al., 2000).
However, there have been only few evaluation studies focusing on mediating mechanisms in
the area of peer influences. Cuijpers (2002), in reviewing the existing literature, reports that
besides the promotion of skills and the increase in knowledge after participation, a reduction
of peer influence in adolescents’ decision making processes was identified as a potential
mediator of positive program effects on substance use. More specifically, studies from the
1990s showed that social acceptability, friends’ reactions to use (Botvin, G., Baker,
Dusenbury, Botvin, L. & Diaz, 1995), perceived peer reactions to use (MacKinnon et al.,
1993), or perceived acceptability of substance use (Donaldson, Graham, & Hansen, 1994)
acted as mediators of program effects. Evidence for resistance skills towards the offer of
substances as program mediator, in contrast, was rather weak (e.g., Hansen & McNeal, 1997;
Wynn, Schulenberg, Maggs, & Zucker, 2000). More recent evaluation studies showed that
perceived peer influence mediated the prevention program effects (Komro et al., 2001;
Orlando, Ellickson, McCaffrey, & Longshore, 2005), so did normative beliefs of prevalence
rates, friends’ consumption behavior and encouragement to use (Liu, Flay, & Aban Aya
Investigators, 2009). Finally, Botvin and Griffin (2004) demonstrated the importance of Life
Skills, such as assertiveness or self-confidence as mediators of program effects.
The vast majority of studies on mediators of program effectiveness relied on U.S. samples;
cultural differences (e.g., regarding prevalence rates in early adolescence, or acceptance of
smoking in youth) may limit the transfer of U.S. findings to the European context. In addition,
most studies in this field investigated samples in mid to late adolescence rather than early
adolescence, while early adolescence seems to be a particularly important life period to
substance use because most users in Europe initiate consumption at this time in the context of
peers (BZgA, 2011), who are especially influential for smoking initiation (e.g., Chassin et al.,
1990). Against this background, we aimed at investigating the role of competencies conducive
to effective peer interactions (i.e., stability against groups, self-confident behavior), and
yielding to peer-pressure in explaining the program effects of a Life Skills program on early
adolescent smoking, investigated in a German context.
Hypotheses
This evaluation study based on the investigation of a longitudinal sample including treatment
and control group, and had two goals. First, we examined the individual trajectories of
tobacco use in adolescents between 10 and 14 years of age as a function of participation in a
Life Skills program. Tobacco use was assessed in terms of the frequency of smoking in the
last 30 days and we assumed that the frequency of smoking could be sufficiently well
described by a linear growth model. As the Life Skills program was supposed to postpone
substance use in early developmental stages and encourage a lower age-typical increase
during adolescence, we hypothesized that students in the intervention group would report a
significantly slower increase in smoking as compared to students in the control group
(Hypothesis 1).
The second and central goal of this study was to investigate possible mediating processes in
the area of competencies relevant in the peer context that were responsible for the supposedly
positive program effect. In other words, we were interested in describing the way in which the
intervention status had an effect on tobacco use through the influence of theoretically selected
mediating variables. As mediator variables we investigated conditions conducive to effective
social interactions within the peer group: self-concept on stability against groups, knowledge
about self-confident behavior, and yielding to peer-pressure. All three competencies reflect
central learning goals of the program under investigation. We hypothesized that the three
constructs represent significant mediators of the effects of the Life Skills program on tobacco
use in early adolescence (Hypothesis 2).
Method
Sample
The original sample consisted of N = 2,464 students who have participated on at least one of
the five measurement occasions. At the first four measurement occasions, 61.7 to 68.7% of
these students took part in the assessments. Participation, however, dropped to 56.2% at the
fifth measurement occasion. From the full sample, 55.2% were in the intervention group and
44.8% in the control group. There were 49.3% boys and 50.7% girls with a mean age of M =
10.48 (SD = 0.64) years at pre-test. Approximately six out of ten participants attended the
college-bound school track (i.e., Gymnasium) whereas the others attended the vocational
school track (i.e., Regelschule).
There were no significant differences between the intervention group and the control group at
the pre-test on various background variables including the number of siblings, t(1629) = 1.15,
p = .25), the subjective evaluation of the families’ financial standing, t(1649) = 1.11, p = .27,
height, t(1653) = .68, p = .49, weight, t(1635) = 1.40, p = .16, and pubertal status in terms of
self-reported growth of pubic hair, t(1619) = .91, p = .36. We found no significant group
differences on initial substance use, i.e. frequency of tobacco use, t(1672) = .52, p = .61 and
alcohol consumption at the last drinking occasion t(1655) = .96, p = .34, and one potential
mediator variable, i.e., knowledge of self-confident behavior, t(1691) = .85, p = .39. However,
students in the intervention group were younger (M = 10.44 years) compared to the control
group (M = 10.54; t(1685) = 3.37, p < .01). Also, there were more boys in the intervention
group (50%) as compared to the control group (44%; t(1690) = 2.33, p < .05). Furthermore,
the students from the intervention group reported lower self concept of stability against
groups (M = 3.90 vs. M = 4.04; t(1671) = 3.56, p < .01) and more yielding to peer pressure (M
= 1.74 vs. M = 1.67; t(1634) = 2.08, p < .05) as compared to the students from the control
group.
Intervention
IPSY (Information + Psychosocial Competence = Protection) is a universal school-based life
skills program that aims to delay the onset and to reduce the normative increase in the
consumption of alcohol and tobacco in early adolescence (Weichold, 2007). The program is
based theoretically on the model for Life Skills education by the World Health Organization
(WHO, 1997) and developmental psychological models on the aetiology of youth problem
behavior, as well as empirical findings on risk and protective factors for substance misuse
(e.g., Petraitis, Flay, & Miller, 1995). IPSY is a comprehensive program that combines the
training of general, intra-personal and inter-personal life skills (e.g., self-awareness, coping
strategies, assertiveness, or communication skills) with instruction on substance-specific skills
(e.g., resistance to peers offering substances). In addition, knowledge concerning alcohol and
tobacco use (e.g., accurate prevalence rates) is conveyed in an age-appropriate manner.
Additionally, IPSY focuses on the promotion of positive school involvement, and structured
leisure activities. The intervention primarily uses interactive methods (e.g., role plays, group
discussion) that have been shown to be the most effective instruction technique in the context
of prevention (see Tobler & Stratton, 1997). It is implemented by teachers who have been
trained in a one-day facilitator workshop before each of the three program parts in grades 5, 6,
and 7, and who use a comprehensive manual. Teachers are trained to be aware of the positive
characteristics of each student and to work with positive reinforcement strategies in order to
promote the acquisition of skills.
Since IPSY is a primary prevention program, it is delivered to adolescents before they start to
experiment with the use of substances. As the average age of substance use initiation in
Germany is around 12 years, the program was developed for students in grade 5 (usually aged
10 to 11 years) with booster sessions in grades 6 and 7. The intervention in grade 5 consists of
15 basic lessons (10 à 90 minutes and 5 à 45 minutes) and there are seven booster lessons (4 à
90 minutes and 3 à 45 minutes) in grade 6 and 7 each in order to practice the learned skills
within age-typical risk situations. Process evaluation was very satisfactory with regard to
fidelity of implementation and acceptance by the students (see Weichold, 2007).
Design
This evaluation study used a quasi-experimental prospective intervention-control group
design with five measurement occasions and school-wise assignment to the respective groups.
Between pre-test (fall of 2003) and post-test (spring of 2004) there was an interval of
approximately half a year. Three follow-up measurements were gathered within an interval of
approximately one year each (spring of 2005 until spring of 2007). The study had to be
approved by the Thuringian State Ministry of Culture and Education, and schools participated
on a voluntary basis. A letter was sent from the Ministry to all 403 schools offering the two
main tracks (Regelschule and Gymnasium) of the federal state of Thuringia inviting them to
participate in a presentation by the research group on an intervention program against
adolescent substance misuse. As schools have been receiving similar invitations on a regular
basis, or may have been already involved in similar activities, the response rate was usually
rather low and only 40 schools accepted the invitation. Reasons given for participation varied
and included, among others, a general interest in intervention programs, specific interest in
substance misuse at schools, and the enhancement of school prestige. During the presentation,
teachers were introduced to the general framework of the IPSY program and to the rules of
participation which included cooperation in an evaluation study. They were then asked to
decide together with the school’s principal whether they wanted to implement the program in
their schools, and whether they would be willing to take part in the evaluation study. At the
end 23 schools out of 40 were selected at random to form the intervention group for the
evaluation study. Control schools were recruited at random from the remaining 363 schools of
the state. Finally, 21 schools agreed to form the control group. One-third of them had already
participated in interventions in the past and, interestingly, the share was the same among our
intervention schools.
The IPSY program was implemented as part of the regular school curriculum. Parents were
informed in the run-up to the project via program presentations and letters. They were then
asked to give consent to their child’s participation in the evaluation part of the study. Parents
of only two students refused to take part in the data collection. The students completed an
anonymous questionnaire of about 60 minutes’ length, administered by project staff or trained
teachers at each measurement occasion in the classroom. At the first measurement occasion,
project staff showed the students how to fill out the questionnaire and answered further
questions. Study participants in both the intervention and the control group received small
incentives for filling out the questionnaires at each wave of data collection (e.g., a pen with
the study logo).
Measures
Intervention Status. Participation in the IPSY program was treated as a dummy-coded variable
where 0 referred to the control group and 1 to the intervention group.
Tobacco Use. At each measurement occasion students were asked how often they had smoked
in the last 30 days. The response categories were “never”, “less frequently than once in a
month”, “once in a month”, “once a week”, “several times a week”, and “on a daily basis”.
The categories were re-coded to reflect the number of days in a month on which the
adolescents presumably smoked, with 0 indicating the “never” category and 30 “on a daily
basis”. As could be expected, average frequency of tobacco use was increasing from M1 = .43
(SD1 = 2.80) over M2 = .96 (SD2 = 4.43), M3 = 2.18 (SD3 = 6.88), and M4 = 4.43 (SD4 = 9.90)
to M5 = 5.51 (SD5 = 11.06), meaning that smoking was virtually non-existent at the pre-test
measurement and increased to approximately five or six days in a month at which students
aged 14 years smoked on average. Retest correlations between single measurement occasions
also systematically increased from r = .43 between pre-test and post-test to r = .66 between
the last two measurement occasions. This finding indicates an incremental consolidation of
smoking behavior throughout young adolescence and, in comparison with other studies, also
supports the validity of the measure used. In fact, Brener et al. (2002), for instance, have
found an average retest reliability of κ = .69 for different measures related to tobacco use in a
large survey on youth risk behavior, although the adolescents in that study were from grade 9
to 12 and thus probably more established smokers, and the retest interval was only two weeks.
Self-Concept on Stability against Group Influences. Self-concept on the stability against
group influences was measured by a subscale of the Frankfurt Self-Concept Scales
(Deusinger, 1986). Stability against groups relates to cognitions and emotions of an individual
in interaction with others (primarily peers, but also those in authority) and skills to
communicate one’s own standpoint and attitudes effectively. Information on twelve items was
gathered, of which two were reverse coded. Examples of the items are “It is hard for me to
advance my own view in front of a group”, “I do not feel so confident in a group because
others often have more ideas than I have”, or “It makes me feel uncomfortable when I have
the impression that someone has got an opinion different from mine”. Students were asked to
rate the items on a 6-point Likert scale. Internal consistency of the mean-composite scales
ranged from .69 < α < .89 with lower values at the beginning of the study. The mean
endorsement to the items answers increased from M1 = 3.92 (SD1 = .83) over M2 = 4.05 (SD2 =
.86), M3 = 4.21 (SD3 = 0.90), and M4 = 4.24 (SD4 = 0.90) to M5 = 4.34 (SD5 = .90) and stability
raised from r = .46 between pre-test and post-test to r = .60 between the last two measurement
occasions.
Knowledge about Self-Confident Behavior. Knowledge on self-confident behaviors was
assessed with six self-developed items that described self-confident, aggressive or
unconfident behaviors as taught within the program. Students were given examples of
behavioral styles and they had to indicate whether the examples represented self-confident or
aggressive behavior. Examples are “looking the counterpart in the eyes” (indicating selfconfident behavior) or “not giving any explanations” (indicating aggressive behavior). The
number of correct answers was counted to form an indicator for knowledge on self-confident
behaviors. The average number of right answers increased from M1 = 1.91 (SD1 = 1.28) over
M2 = 2.29 (SD2 = 1.37), M3 = 2.65 (SD3 = 1.43), and M4 = 3.02 (SD4 = 1.45) to M5 = 3.10 (SD5
= 1.45) and the retest reliability between adjacent measurement occasions rose from r = .35
between pre-test and post-test to r = .54 between the fifth and the sixth measurement
occasion.
Yielding to Peer Pressure. Peer pressure was measured by a scale of eight items proposed by
Santor, Messervey, and Kusumakar (2000). Item wordings were, for instance, “If other
students want something from me, I can hardly say no”, “When my friends are drinking
alcohol it is difficult for me not to join them”, or “Sometimes I do stupid or dangerous things
just because other want me to do so”. Students were asked to rate how much the items applied
to them on a 5-point Likert scale and higher values meant more yielding to peer pressure, or
less peer pressure resistance. Internal consistency was satisfactory and ranged between .67 < α
< .83 with the lowest value at the pre-test measurement. Average endorsement to this scale
was rather low (M1 = 1.74, SD1 = .66; M2 = 1.80, SD2 = .66; M3 = 1.78, SD3 = .66; M4 = 1.93,
SD4 = .71; M5 = 2.01, SD5 = .68) as was the stability between adjacent measurement occasions
(.35 < r < .43).
Statistical Analyses
We used the framework of latent growth modeling (see Bollan & Curran, 2006; Muthén &
Curran, 1997) to identify linear trajectories of intra-individual change in the frequency of
tobacco use and to predict this change by intervention status. A latent growth model with
intervention status as a covariate was used to address Hypothesis 1. It was hypothesized that
participation in the IPSY program would predict a slower increase of tobacco use over time
(i.e., slope). Concerning the prediction of the intercept of tobacco use, we expected no effect
of participation in the IPSY program as such an effect would indicate shortcomings in the
random assignment to the intervention and control groups.
In order to test the hypothesized mediation effects we modeled the outcome variable
simultaneously with each of the supposed mediating variables in a parallel process latent
growth curve model as suggested by Cheong, MacKinnon, and Khoo (2003). This approach
allowed us to investigate how the mediation process affected the progression of tobacco use
as a function of participation in the IPSY program. As can be seen in Figure 1, the parallel
process model consists of basically three parts. The first part summarizes the manifest
longitudinal measurements of the mediator (M1, M2, ...) into two growth components: the
intercept at the first measurement occasion (η1) and a linear slope (η2). Both the intercept and
the slope component has got a mean representing the average group trajectory and a variance
representing inter-individual variation around the average trajectory. It is assumed that the
longitudinal change in the mediator can be sufficiently described by the two growth
components. Accordingly, the manifest longitudinal measurements of the outcome variable
(Y1, Y2, …) are described in terms of an intercept (η3) and a slope (η4) which again have a
mean and a variance and provide a sufficient description of longitudinal change in the
outcome variable. The third part of the model simply comprises a manifest predictor of
intervention status (X) which in our case is a dichotomous variable carrying the information
whether a participant belonged to the intervention or the control group.
By setting up structural paths between the three parts of the model it is possible to test the
relationships between intervention status, longitudinal change in the mediator, and
longitudinal change in the outcome. For the purpose of a mediation analysis, three paths are of
particular relevance. First, the path from intervention status to the slope of the mediator
variable (α) represents the effect of the intervention on change in the mediator. If it is
significant, it shows that the slopes of the mediator were significantly different for the
intervention and the control group. The intervention group might, for instance, more strongly
increase their knowledge about self-confident behavior over time. Second, the path from the
slope of the mediator to the slope of the outcome (β) represents the association between
change in the one variable with change in the other variable. A significant path might, for
instance, indicate that children whose knowledge about self-confident behavior increases
more strongly increase their tobacco use less steeply. Finally, the path from intervention status
to the slope of the outcome (τ') represents the residual intervention effect that cannot be
explained by the mediator. If path τ' is not significant but paths α and β are, one can assume
that the effect of the intervention was totally mediated by the mediator. Mediation itself is
tested directly by assessing whether the indirect effect from intervention status via the slope
of the mediator to the slope of the outcome (αβ) is significantly different from zero. If this is
the case one can assume that changes in the outcome are a function of changes in the mediator
which in turn is influenced by the intervention status.
Growth models in general have been advocated as the best available method for addressing
individual change over time (e.g., Rogosa, 1988). They are particularly well suited for
investigating the longitudinal relationship between a mediator and an outcome when one or
more of these variables exhibits a meaningful trajectory of change (Selig & Preacher, 2009),
as is the case for adolescent tobacco use. However, it has to be noted that when using parallel
process models the direction of effects is not tested empirically but rather assumed
theoretically, as both the mediator and the outcome are assessed simultaneously and the
mediator is not assigned randomly (see Cheong et al., 2003). Such modeling thus requires a
strong theory as it is not possible to decide empirically via model fit whether the assumed
mediator mediates the program effect to the assumed outcome or whether the assumed
outcome mediates the program effect to the assumed mediator.
For all calculations, we used the Mplus software version 6.1 (Muthén & Muthén, 2010).
Missing data were treated by full information maximum likelihood for the growth curve
models (see Enders, 2010; Schafer, 1997). Analyses were conducted separately for the three
potential mediators (i.e., self-concept on stability against groups, knowledge on self-confident
behavior, and yielding to peer pressure). All growth models were specified taking into
account the different measurement intervals between the pre-test and the post-test on the one
hand, and between the follow-up measurements on the other.
Results
Program Effect on Frequency of Tobacco Use
We hypothesized that the program IPSY has an intervention effect on adolescent tobacco use
in terms of a slower increase in frequency of tobacco use in the intervention as compared to
the control group (H1).The linear latent growth model describing the frequency of tobacco
use conditional on the intervention status fit the data reasonably well, χ²(13) = 140.98, p < .01,
RMSEA = .065, SRMR = .058 and thus we accepted this model. Both the intercept (M = 0.43)
and the slope of tobacco use (M = 1.74) were significantly different from zero (p < .01) and
the two variance components were positively correlated (r = .31; p < .01). The effect of the
intervention status on the intercept of tobacco use was small (β = -.02) and non-significant,
while the effect of the intervention status on the slope of tobacco use was β = -.09 (p < .01).
Whereas the former finding suggested that the intervention group was not different from the
control group in terms of tobacco use before treatment, the latter finding suggested a slower
increase in the frequency of tobacco use in the intervention group as compared to the control
group during the course of the study, which confirmed Hypothesis 1. The beta weight of the
slope of tobacco use on intervention status translates into an effect size of ES = -.19 which
corresponds to a “small” effect size according to Cohen (1988), but is comparable with effect
sizes of other interactive programs (see Tobler & Stratton, 1997).
Mediator Analyses
In our second hypothesis (H2), we expected that skills needed to resist peer influences (i.e.,
stability against groups, self-confident behavior) and yielding to peer pressure mediate the
program effect of IPSY on frequency of tobacco use. In the following section, results on
mediation analyses were presented separately by the three variables.
Self-Concept on Stability against Groups. The parallel process model, based on N = 2,362
observations, fit the data reasonably well, χ²(49) = 328.01, p < .01, RMSEA = .049, SRMR =
.067, and was thus accepted. Intercept (M = 4.02) and slope (M = .09) of the mediator were
significantly different from zero (p < .01). The latent regression paths of this model are
presented in Table 1. First of all, there is a significant direct effect of intervention status on
the slope of tobacco use (τ') indicating that, if at all, stability against groups can only be a
partial mediator of the program effect. The intervention seems to have positively influenced
the slope of stability against groups (α) which in turn is unrelated to the slope of tobacco use
(β). Taking the two paths together, the indirect effect of IPSY through the variable stability
against groups on smoking is not significant, αβ = .01, p = .22, thus, in contrast to hypothesis
2, self-concept on stability against groups did not act as mediator of the program effects of
IPSY on adolescent smoking. In addition, there is a significant effect of intervention status on
the intercept of the mediator (γ1) which suggests the intervention group was lower on stability
against groups at baseline as compared to the control group.
Knowledge of Self-Confident Behavior. The parallel process model, based on N = 2,376
observations, fit the data reasonably well, χ²(49) = 321.38, p < .01, RMSEA = .048, SRMR =
.049, and was thus accepted. Intercept (M = 2.00) and slope (M = .32) of the mediator were
significantly different from zero (p < .01) which indicates the knowledge of self-confident
behavior increases over time. Again, the central parameters of this model can be found in
Table 1. It is noteworthy that the intervention increased knowledge of self-confident behavior
(α = .11; p < .05) which in turn has a substantial negative effect on the slope of smoking (β = .28; p < .01). The indirect effect (αβ = -.03) is also significant (p < .05) so that, in line with
hypothesis 2, increased knowledge of self-confident behavior mediates the effect of IPSY on
the increase in tobacco use. Furthermore, we found that higher levels of knowledge at
baseline were also associated with less smoking (γ4) which affirms that self-confident
behavior represents a powerful protective factor against adolescent smoking.
Yielding to Peer Pressure. The parallel process model, based on N = 2,357 observations fit the
data reasonably well, χ²(49) = 278.63, p < .01, RMSEA = .045, SRMR = .054, and was thus
accepted. We found that both the intercept (M = 1.73) and the slope (M = .09) of yielding to
peer pressure were significantly different from zero (p < .01). As can be seen in Table 1, IPSY
participants more likely decreased their yielding to peer pressure (α = -.14; p < .05) as
compared to the control group. High yielding to peer pressure, in turn, was positively
associated with increasing tobacco use (β = .36; p < .01). The two effects together resulted in
a significant indirect effect of IPSY on tobacco use (αβ = -.03; p < .05), which suggests, in
line with hypothesis 2, that yielding to peer pressure acts as mediator to explain the positive
program effects of IPSY on smoking. We furthermore found that a higher level of yielding to
peer pressure at baseline predicted a higher increase in the frequency of smoking throughout
adolescence (γ4). This implies that yielding to peer pressure resembles an important risk factor
for adolescent smoking behavior which as early as around age 10 puts children at risk for an
unfavorable trajectory of tobacco use during adolescence.
Discussion
This study investigated the effects of the Life Skills program IPSY on tobacco use in a sample
of young adolescents from Germany. While the majority of existing studies did not include a
long-term perspective and focused on older age groups, effects were analyzed over a fouryear study interval from age 10 to 14. We found, in line with our hypotheses, a significant
effect of program participation on the slope of tobacco use over time, indicating that IPSY
reduced the age-typical increase in smoking frequency from early to mid adolescence. The
effect size (.19) is low, but according to Tobler et al. (2000) it lies in the upper range of what
can be expected of a school-based interactive Life Skills program. Consequently, this program
can be deemed an effective strategy to prevent youth smoking behavior during early and mid
adolescence.
We were in particular interested in whether competencies conducive to effective peer
interactions and for resisting peer influence in the intra- and interpersonal domain (selfconcept on stability against groups, knowledge on self-confident behavior, and yielding to
peer-pressure) cause the program effects on smoking. This expectation was based on earlier
theoretical and empirical work stressing the importance of peer influences as risk factors for
adolescent smoking behavior (Kobus, 2003; MacKinnon et al., 2002). First, we tested whether
or not the program influenced the potential mediators in the area of peer interactions
positively. We found that the Life Skills Program IPSY was effective in promoting
competencies relevant for effective peer interactions, namely stability against groups, selfconfidence, and resisting (vs. yielding) to peer-pressure. This was evidenced by the fact that
program participation significantly predicted the slope of these variables over time. This result
resembles findings concerning other Life Skills programs which aim at the prevention of
adolescent substance use and also found positive effects on skills and competencies conducive
for peer interactions (e.g., Botvin & Griffin, 2004; Botvin, Griffin, Diaz, & Ifill-Williams,
2001; Bühler, Schröder, & Silbereisen, 2007).
Our findings demonstrated that competencies relevant for effective peer interactions can be
changed via the Life Skills program over several years, instead of the usually shorter time
periods as shown in earlier research. This was probably the case because skills are practiced
and applied in age-typical challenging situations within same-aged peer groups in a
systematic fashion over three years of program implementation. Thereby, suggestions for
optimal design of Life Skills curriculums across several years, as introduced by WHO (1997),
were realized for program development. The lessons dealing with assertiveness and selfconfidence of the IPSY program start out with the facilitation of basic skills which
subsequently are trained within more and more specific situations with regard to substance
use during the subsequent booster sessions in grades 6 and 7. Consequently, a curriculum
designed to promote skills to deal with peer influences implemented across several years of
education seems to be particularly effective to improve competencies at long-term.
However, knowing that a program is effective to promote skills for resisting peer influence
does not necessarily mean that these skills indeed are responsible for a less pronounced
increase in consumption of cigarettes observable after taking part in the intervention.
Consequently, mediation analyses were performed to investigate whether the change in risk
and protective factors transmits the effects of group assignment on change in substance use
(Howe et al., 2002). Such analyses were rarely conducted based on longitudinal, well
designed intervention studies including a randomization element. The current study tried to
fill this gap, thereby demonstrating that the higher increase in knowledge on self-confident
behaviors and the lower increase in yielding (or higher resistance) to peer pressure as
compared to the control group mediated the program effects on the frequency of smoking
cigarettes in German students during early and mid adolescence. This result is in line with
findings on other Life Skills programs which showed for somewhat older students that selfconfidence, resistance to peer pressure, and a reduction in peer influence were mediators of
program effects on substance use (e.g., Botvin et al., 1995; Orlando et al., 2005). In addition,
Bühler et al. (2007) showed that knowledge on skilled behavior such as on assertiveness
partly mediated the effect of a Life Skills program on smoking during early adolescence.
Thus, both, knowledge acquired to act self-confidently, and lower yielding to peer-pressure to
engage in deviant and unhealthy behaviors seem to be important protective factors against
youth tobacco use from early to mid adolescence.
Against our expectations, we found that self-concept on stability against groups was
positively influenced by the program, but did not mediate the effect on tobacco use. Although
based on somewhat different measurements, similar results were obtained in other studies
with older U.S. American samples (Cujipers, 2002; Orlando et al., 2005). However, it could
be that a positive self-concept contributes to the ability to resist pressure within peer
interactions indirectly (i.e., youth with a more positive self-concept are better able to
implement peer refusal strategies in their peer context; Epstein, Griffin, & Botvin, 2000). This
line of argumentation suggests that program components focusing on these issues are not
necessarily inefficient. Consequently, further studies are needed to explore the role of the
promotion of general intrapersonal Life Skills in explaining effects of Life Skills programs in
more depth.
This study has strengths but also several weaknesses. Its strengths include the randomized
quasi-experimental study design including an intervention group and a control group as well
as assessments covering four years of development. Another positive aspect of this study is
that the selection of possible mediators of program effects was based on a strong theoretical
and empirical basis (Cuijpers, 2002; Kobus, 2003; Pandina et al., 2010). In addition, data
were analyzed using especially suitable statistical methods (i.e., the framework of complex
longitudinal growth modeling; Bollan & Curran, 2006). The parallel process growth modeling
used in testing mediation effects (Cheong et al., 2003) enabled us not only to provide a gross
assessment of whether the program worked or not. More importantly, it allowed us to identify
the underlying mechanism of how the program achieved its effects by capturing longitudinal
change in the mediating variables and the outcome, rather than simple differences in these
variables before and after the intervention. Several researchers have argued that longitudinal
growth modeling is superior for answering questions about longitudinal change whereas
assessing pre- and post-intervention scores might even prove inadequate in many research
contexts (e.g., Rogosa, 1988; Rogosa, Brandt, & Zimowski, 1982; Willet & Sayer, 1994).
Major advantages of our approach were the estimation of individual differences in change
over time, the simultaneous modeling of both the mediator and outcome process, the
advantage of obtaining an unbiased estimate of the average long-term treatment effect (see
Raudenbush, 2001), the high robustness of the method against short-term fluctuations of
scores between two single time points, and the use of the maximum of information on
individual change that was available.
Limitations of this study include the fact that we covered only three aspects of competencies
conducive to effectively interacting with peers and resisting peer pressure. It may well be that
other facets of interpersonal behavior or aspects of self-concept which were not measured
within this study might be also important to mediate the program effects. Although we found
that the direct effect of program participation disappeared by introducing the mediators (i.e.,
knowledge on self-confident behaviors, yielding to peer-pressure) into the model, we cannot
conclude from this study that the other program components included in the IPSY program
are ineffective. The facilitation of broad Life Skills, creating an unusual learning environment
with new rules on how to interact with each other, and the open discussion of critical topics,
as it is usual for Life Skills programs, might represent an important basis for learning and
practicing how to resist peer pressure. Higher school involvement and better classroom
climate as stimulated by the IPSY program, for instance, have been shown to act as mediators
of program effects on alcohol use (Wenzel, Weichold, & Silbereisen, 2009). Thus, further
research should include more (also qualitative) measures on Life Skills and school
environment.
To conclude, this study is one of the few examining mediation effects of a Life Skills program
on tobacco use based on a longitudinal study of students from early to mid adolescence,
applying modern and complex techniques for data analysis. The results stress the importance
of the promotion of skills relevant to interacting with peers and resisting peer influence to
effectively combat early tobacco use in young adolescents and its various negative health and
psychosocial outcomes in later life (Mathers et al., 2006). As this study showed, low selfconfidence and high yielding to peer pressure seem to reflect major risk factors for smoking in
early adolescence that can be changed by a Life Skills program, which appears to be
responsible for positive effects of the IPSY program SY on adolescent smoking. In addition,
although the effect size suggests a “small” intervention effect of the program, this is
nevertheless meaningful given the fact that IPSY is a universal prevention program for entire
population groups. Consequently, it makes sense that this program be widely distributed in
German schools, and further dissemination will be proposed in the future. Along with this, a
new part of the program manual (i.e., booster session for grade 8) is currently under
development wherein the promotion of the effective “ingredients” of self-confidence and
resistance to peer pressure will be central topics to ensure positive long-term effects.
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Table 1: Selection of parameter estimates of the parallel process growth curve models.
Stability against Groups
Self-Confidence
Yielding to Peer Pressure
α
.12 **
.11 **
-.14 **
β
.09
-.28 **
.36 **
τ'
-.10 **
-.05
-.04
γ1
-.08 **
.03
.01
γ2
.06
-.11
.05
γ3
-.02
-.02
-.02
γ4
-.06
-.13 **
.30 **
Note. Standardized estimates, notation of parameters corresponds with Figure 1; α = slope of
moderator on intervention status; β = slope of outcome on slope of moderator; τ' = slope of
outcome on intervention status; γ1 = intercept of moderator on intervention status; γ2 = slope
of mediator on intercept of outcome; γ3 = intercept of outcome on intervention status; γ4 =
slope of outcome on intercept of mediator; * p < .05; ** p < .01
Figure 1: A parallel process latent growth model for mediation. Reprinted with permission
from Cheong, J., MacKinnon, D. P., & Khoo, S. T. (2003). Investigation of mediational
processes using parallel process latent growth curve modeling. Structural Equation
Modeling, 10, 238-262.