Diskussion of the paper by Mai Stafford et al. 2007„Pathways to obesity:
identifying local, modifiable determinants of physical activity and diet“
Commentary by Sven Voigtländer
From my background I am a Master of Public Health working for the work group
“Epidemiology & International Public Health” at the School of Public Health in Bielefeld
where we are also focusing on the interplay of contextual and compositional effects on health.
I am glad to have been asked to discuss this paper because from a German perspective the
current state of research regarding contextual effects on health can be considered as in its
beginnings. Most of the studies so far are on an ecological basis applying general measures of
morbidity and mortality as outcomes. Thus it is not possible to differentiate between
compositional and contextual effects. The most recent studies of this type have been provided
by Angela Queste and myself.
In her study Angela Queste linked age-adjusted mortality rates with unemployment rate,
percentage of high-school graduates and population density on the German district level. On
the basis of a multiple linear regression model she was able to explain 60% of the district
variation in age-adjusted mortality rates whereas the explanatory power of unemployment rate
was by far the highest.
In my own study on the basis of German Raumordnungsregionen I was using an index of
structural weakness comprising gross domestic product per capita, unemployment rate and
internal migration balance in order to explain regional variation in the SF12 summary scores.
Doing so I was able to identify a gradient of structural weakness regarding regional SF12
summary scores as well as sex-specific differences. However the level of analysis, namely the
German Raumordnungsregionen, was too aggregated to capture local disparities.
As far as I know only one multi level study by Wolf (2004) on the basis of Cologne
municipalities has been published in Germany. According to this study morbidity was
especially high in deprived areas. However, in controlling for individual variables (age, sex,
family status and social class) only 5% of the morbidity disparities could be ascribed to
contextual effects and this was statistically insignificant.
Taking this as a German baseline the paper of Mai Stafford et al. as well as other AngloAmerican research publications are especially interesting to further research and an
understanding of contextual effects on health in Germany. The paper as such is very helpful in
several ways. First, it brings together various local social and physical environmental
characteristics which have been associated to health in the past but not in their complex
relationships. Second, it explicitly focuses on modifiable features of the residential
environment and as such it is strongly oriented towards health promotion practice and
possible interventions. Third, it applies the very innovative method of structural equation
modelling which not only combines regression, factor and path analysis but also forces the
researcher to carefully reason a causal model beforehand.
Nevertheless I also want to raise some theoretical and methodological issues for discussion.
The authors raise two major shortcomings of previous studies: 1. the weakness of theoretical
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models and 2. the use of a limited number of indicators to characterise neighbourhoods as
well as the non-observance of their complex interaction. I think that – due to several reasons –
the paper itself struggles with these shortcomings also.
In the underlying structural model the measures of local infrastructure and services as well as
neighbourhood socio-relational characteristics appear somewhat independent although we
know that individual socioeconomic variables have a variation effect on their exposure. I
don’t know how far this can be compensated by the age-, sex- and SES-adjustment of the
outcome obesity.
Apart from that, structural equation models – and above that using cross-sectional data – are
not able to answer questions of causality. Therefore the application of longitudinal data to
differentiate the temporal sequence of events or – as mentioned by the authors – in-depth
studies are indispensable.
Furthermore the structural model shows that the variables “No. Police officers“ and „SES“
have an opposite path coefficient than expected and that the path coefficients of several
variables are insignificant. Hence, it is indicated to validate the empirical structural model
using new, different data, i.e. from another European country.
Another issue pointing to the lack of available data is the difference between theoretical
model and structural model. Whereas the theoretical model regards good diet and physical
activity as intermediate health behaviours the structural model cannot accommodate these
with the effect that neighbourhood disorder and sports participation rate remain the only
intermediate variables. However, increasing quality of data and increasing access to various
data sources – also in the German context – offer an optimistic outlook to the future.
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