2.2. Selective daily mobility bias in GPS studies
The description of behavioral contexts (e.g., of the places
actually used to exercise) can help plan the provision of healthenhancing
services (Duncan and Mummery, 2007; Lachowycz
et al., 2012; Quigg et al., 2010). Moreover, this descriptive
information is useful to generate hypotheses on environmental
resources that support behavior; these causal hypotheses then
need to be formally tested through appropriate designs. Our focus
here is on such causal inferences on environmental effects (‘‘does
the presence of X in the environment influence the behavior of
people who live, work, or spend time nearby?’’).
In the reviewed studies, exposures to the built and food
environments were determined around valid GPS points, including
places where individuals specifically go to practice the
behavior investigated (e.g., to buy or eat specific foods or to
practice physical activity). With such measures, participants with
a particular taste for energy-dense food that leads them to eat
several days a week in fast-food restaurants would be classified as
often ‘‘exposed’’ to a significant density of fast-food restaurants.
Similarly, people with advanced knowledge on the benefits of
physical activity, positive attitudes toward exercise, and a suffi-
cient self-efficacy to convert intentions into regular physical
activity more frequently visit sport or recreational facilities and
would therefore appear as more ‘‘exposed’’ to physical activity
opportunities. Such intrapersonal factors that encourage specific
study particip