METHODS
We focused on research investigating the
effects of sugar-sweetened beverages; diet
and artificially sweetened beverages are
noted only in certain cases for comparison
purposes. We conducted a computer search
through MEDLINE and PsycINFO using the
key terms “soft drink,” “soda,” and “sweetened
beverage.” We identified articles that assessed
the association of soft drink consumption with
4 primary outcomes (energy intake, body
weight, milk intake, and calcium intake) and
2 secondary outcomes (nutrition and health).
We identified additional articles by searching
each article’s reference section and the Web
of Science database. Finally, we contacted the
authors of each included article with a request
for unpublished or in-press work, and
we asked each author to forward our request
to other researchers who might have relevant
work. Our searches yielded a total of 88
articles that were included in the present
analysis.
There is a great deal of variability in research
methods in this literature. Studies
vary in their design (i.e., cross-sectional, longitudinal,
or experimental studies), sample
characteristics (e.g., male vs female, adults vs
children), and operational definitions of independent
and dependent variables. Because
such heterogeneity of research methods is
likely to produce heterogeneity of effect sizes
across studies (an effect size represents the
magnitude of the relationship between 2 variables),
we took 2 steps to assess the impact
of research method on outcome.
Initially, for each primary outcome (energy
intake, body weight, milk intake, and calcium
intake), we assessed the degree of heterogeneity
of effect sizes by testing the significance
of the Q statistic, which is the sum of the
squared deviations of each effect size from
the overall weighted mean effect size. We did
not assess the degree of heterogeneity for