Lab #9 - Statistical Tests
Review:
1. Correlation
 Used when interested in assessing the strength
of association between two variables
 Used with continuous variables
  is the Greek letter rho, which is the population
parameter tested in hypotheses (remember what
parameters are from intro statistics?)
 r is the sample statistic that corresponds with 
 correlation is statistically significant if the r
value surpasses the critical value of r (use a
statistical table or computer program)
 Example research hypothesis: Are higher levels
of self-esteem associated with lower levels of
depression (What is the null hypothesis? What
direction correlation would be expected under
the alternative/research hypothesis?)
2. Regression
 Like correlation, used to assess the strength of
association between two variables
 Two differences from correlation:
1. Regression is used when primary
interest is predicting scores, not just
association between all scores
2. Regression is used with one IV and one
DV (e.g., conscientiousness predicting
job performance); it is also used when
there is more than one IV (e.g., ability,
conscientiousness, and interest in the
job predicting job performance), and in
that case it is called multiple regression
– your final project however only has
one IV
 Used with continuous variables
  (beta) is population parameter tested in
hypotheses
 b (slope of regression line) is the sample statistic
corresponding with 
 regression is statistically significant if t-statistic
for b is greater than the critical value of t (use a
statistical table or computer program)
 Example research hypothesis: Does higher selfesteem in middle childhood lead to lower levels
of depression in adolescence? (notice this is
different than correlation in that here we’re
interested predicting scores)
3. Independent samples (between-groups) t-test
 Used to determine mean differences in the
dependent variable for two different groups
 Used with categorical or dichotomous variables
 Only one independent variable with only two
levels/groups
  (mu) is population parameter tested in
hypotheses
 X (x-bar) is sample statistic corresponding with

 t-test is significant if t-statistic for X is less
than/greater than the critical values of t
 Example research hypothesis: Do women have
higher levels of depression on average than do
men (gender defines 2 independent groups, a
continuous measure of depression is the DV)?
New:
4. Analysis of Variance (ANOVA)
 Like t-test, used to determine dependent
variable mean differences between
groups/levels, but can use when there are more
than two groups (which is the same as more
than two levels of your IV)
 Remember, though, you’re still only using one
IV, just there are more than two groups/levels
(e.g., you might have the IV of political party,
with the groups being Democrat, Republican,
and Independent)
 Can use for your final project if you have just
one IV with more than two groups (i.e., one-way
ANOVA). ANOVA can also be used for more
than one IV (i.e. two-way ANOVA, where say
you have political party [3 groups] that may
differ by gender [2 groups] for a 2  3 two-way
ANOVA)
 Independent variable has two or more levels; if
you only have one IV with two levels, though,
use a t-test, even though ANOVA would give
you the same results (and if you have more than
one IV then you aren’t following the directions
for the final project!  )
  (mu) is population parameter tested in
hypotheses
 X (x-bar) is sample statistic corresponding with

 ANOVA is significant if F-statistic is greater
than the critical values of F
 Example research hypothesis: Do psychology
graduate students tend to have higher IQs than
medical students, physics graduate students,
and English graduate students (what is the IV,
what is the DV)?
5. Repeated measures (within-groups) t-test or ANOVA
 Used to test mean differences in the DV for the
same group measured at two or more times
 The t-test involves an independent variable with
two levels; ANOVA involves independent
variable(s) with more than two levels (e.g., use
ANOVA when over a year, the same group of
clients is exposed to each of 4 types of group
counseling [the IV], and for each type of
counseling, the clients’ symptoms [the DV] are
measured).
 Population parameters and sample statistics are
the same for both the between-group t-test and
ANOVA.
 Example research hypothesis for repeatedmeasures t-test: Do people like the taste of Pepsi
more than Coke (where the same people would
taste both types of pop)?
 Example research hypothesis for repeatedmeasures ANOVA: Does exposure to death
metal music leads to better cognitive
performance than exposure to jazz, classical, or
country music (where the same people would
perform a cognitive task [DV] after listening to
each type of music [IV])?
Research Designs and Statistical Tests
What type of control do you have over your independent
variables?
Non-experimental designs
 No control over independent variables
Experimental designs
 Control over independent variables
 Hallmarks: manipulation of independent
variables and random assignment to
groups/ levels
Quasi-experimental designs
 Only partial control over independent
variables.
 Participants are assigned to groups/ levels
by means other than random assignment on
at least one of the independent variables.
- Person by treatment quasi-experiment
- Natural experiments (e.g. tornado
damage vs. no tornado damage)
Does each group receive different treatments/conditions
or same treatments/conditions?
 Different conditions = Between-group design
 Same conditions = Within-group (repeated
measures) designs
- Pretest - Posttest designs
How many independent variables in your design?
 One IV (only one IV for your final project):

t-test

One-way ANOVA (F-test)

Correlation

Regression
 Two:

Two-way ANOVA

Multiple regression
 Three:

Three-way ANOVA

Multiple regression
What type of independent variables in your design?
 Continuous
 Correlation
 Regression
 Categorical
 t-test
 ANOVA
Note that the DV will be continuous no matter which
type of IVs you have
How many levels/groups do your independent
variable(s) have?
 Continuous variables, strictly speaking, have
an infinite number of levels
 With continuous IVs, you include the full
range of scores across a group of
individuals (you could consider each unique
scores as a “level”)
 Categorical variables generally have two or
more levels/groups/conditions/treatments
 2 levels = t-test
 2 or more levels = ANOVA
Example Research Designs and How to test?
Example 1: Hypothesis - Higher levels of alcohol use
tends to result in greater impairment in reaction time.
Three groups of participants are each given alcohol
mixed with orange juice. Each of the three groups
gets a different amount of alcohol that corresponds to
a different blood alcohol level (.01, .05, .10). The
fourth group serves as a control group and only
receives orange juice without alcohol. Each group is
measured on a reaction time task.
1st question: What is the independent variable(s)?
2nd question: Do researchers have control over IV
(manipulation and random assignment)? Full or
partial control?
 So which type of research design?
3rd question: Are groups given different treatments or
same treatments?
 So, between-group design or repeated measures
design?
4th question: How many independent variables?
 So, what kind of tests could be used?
5th: Are they continuous or categorical?
 So, what kinds of tests could be used?
6th question: How many levels/groups in the
independent variable(s)?
 So, what test?
Example 2: Hypothesis - Depressed and non-depressed
people have different explanations for negative life
events only when in a negative mood. Depressed and
non-depressed participants are randomly assigned to
two conditions: positive mood inducing task or
negative mood inducing task.
1st question: What is the independent variable(s)?
2nd question: Do researchers have control over IV
(manipulation and random assignment)? Full or
partial control?
 So which type of research design?
3rd question: Are groups given different treatments or
same treatments?
 So, between-group design or repeated measures
design?
4th question: How many independent variables?
 So, what kind of tests could be used?
5th: Are they continuous or categorical?
 So, what kinds of tests could be used?
6th question: How many levels/groups in the
independent variable(s)?
 So, what test?
Example 3: Hypothesis - Greater involvement with
violent media leads to higher levels of aggression in
adolescents. Adolescents report on both their
involvement with violent media and their aggressive
behavior; adolescents' parents also report on their
children's aggressive behavior.
1st question: What is the independent variable(s)?
2nd question: Do researchers have control over IV
(manipulation and random assignment)? Full or
partial control?
 So which type of research design?
3rd question: Are groups given different treatments or
same treatments?
 So, between-group design or repeated measures
design?
4th question: How many independent variables?
 So, what kind of tests could be used?
5th: Are they continuous or categorical?
 So, what kinds of tests could be used?
6th question: How many levels/groups in the
independent variable(s)?

So, what test?
Example 4: Men and women differ in their attitudes
about capital punishment. Men and women are asked
to complete surveys describing their attitudes about
capital punishment.
1st question: What is the independent variable(s)?
2nd question: Do researchers have control over IV
(manipulation and random assignment)? Full or
partial control?
 So which type of research design?
3rd question: Are groups given different treatments or
same treatments?
 So, between-group design or repeated measures
design?
4th question: How many independent variables?
 So, what kind of tests could be used?
5th: Are they continuous or categorical?
 So, what kinds of tests could be used?
6th question: How many levels/groups in the
independent variable(s)?
 So, what test?
For Project - Methods Section (steps 5 - 9)
Make sure to review Project Guidelines
Step 5: Type of design - talked about that today
Step 6: Sampling plan - talked about this a couple of
weeks ago
- Make sure you define your population (don't
mix up with your sample)
- Describe IN DETAIL how you will sample
your participants (how will you find them,
recruit them, get them to participate, protect
their rights, etc.)
Step 7: Measurement
- Finding measures
- From existing literature that you're using
for intro
- From Tests in Print, etc.
- Make your own
- Reliability and validity information
- Must list no matter where measure comes
from
- Should be good reliability and validity for
you to use measure
- If not listed (or you're making your own),
you must describe how you'll find
reliability and validity
- e.g. test-retest reliability (measure
people twice, correlate)
- e.g. expert judgment of items for
validity
- Describe, again, IN DETAIL, how you
will administer your measures. If
manipulating your IV in experiment,
describe IN DETAIL the manipulation.
Step 8: Statistical procedure - talked about that today
Homework for Lab #9
For each of the five research hypotheses described below, list (a) which type of research
design is employed (non-experimental, experimental, or quasi-experimental), (b) what type
of statistical test you would use to test it (independent (between-groups) t-test, betweengroups ANOVA, repeated measures t-test, repeated measures ANOVA, regression,
correlation), and (c) whether external or internal validity is most threatened (this is from
lecture material not lab). Explain your answers to receive full credit! 
Research hypotheses:
1. People who are on a high-fish diet will perform better on memory tests than people on a
low-fish diet.
2. Children will show higher levels of aggression after playing a violent video game. 7year olds will be interviewed and measured on aggression when they first come into the
study; they will be measured again immediately after playing 2 hours of a violent video
game; and they will be measured one last time 3 days after the game was played.
3. The degree to which someone believes in God relates to his/her level of risk-taking.
Specifically, the more someone believes in God, the more willing he/she will be willing to
take risks in life.
4. People who are relaxed will have a better memory for the events of a crime than people
in a stressed state or a control group. The first group goes through a progressive
relaxation session and is then presented with a short (10-minute) video of a crime that
was recorded on a security camera at a convenience store (called Fredway). The second
group goes through a stress-inducing session – listening to loud music in a room with a
strobe light – and then is presented with the same video. The control group does not go
through any session; they are only presented with the video. After 2 hours, all groups
are given list of events and have to answer true/false which ones occurred.
5. Children will tend to perform slower (more carefully) on a multiplication task when
they are competing with another person to get questions right vs. when they are by
themselves and are told to do as many as they can under timed conditions. Children
will be randomly assigned to the group vs. timed conditions.