GPS or travel diary: Comparing spatial and temporal characteristics of visits to fast food restaurants and supermarkets

<div><p>To assess differences between GPS and self-reported measures of location, we examined visits to fast food restaurants and supermarkets using a spatiotemporal framework. Data came from 446 participants who responded to a survey, filled out travel diaries of places visited, and wore a GPS receiver for seven consecutive days. Provided by Public Health Seattle King County, addresses from food permit data were matched to King County tax assessor parcels in a GIS. A three-step process was used to verify travel-diary reported visits using GPS records: (1) GPS records were temporally matched if their timestamps were within the time window created by the arrival and departure times reported in the travel diary; (2) the temporally matched GPS records were then spatially matched if they were located in a food establishment parcel of the same type reported in the diary; (3) the travel diary visit was then GPS-sensed if the name of food establishment in the parcel matched the one reported in the travel diary. To account for errors in reporting arrival and departure times, GPS records were temporally matched to three time windows: the exact time, +/- 10 minutes, and +/- 30 minutes. One third of the participants reported 273 visits to fast food restaurants; 88% reported 1,102 visits to supermarkets. Of these, 77.3 percent of the fast food and 78.6 percent supermarket visits were GPS-sensed using the +/-10-minute time window. At this time window, the mean travel-diary reported fast food visit duration was 14.5 minutes (SD 20.2), 1.7 minutes longer than the GPS-sensed visit. For supermarkets, the reported visit duration was 23.7 minutes (SD 18.9), 3.4 minutes longer than the GPS-sensed visit. Travel diaries provide reasonably accurate information on the locations and brand names of fast food restaurants and supermarkets participants report visiting.</p></div

Univariate biometric genetic model for binary measures of physical activity in UWTR same-sex twin pairs.

*<p><i>ACE</i> refers to a model that includes additive genetics (A), common environment (C), and unique environment (E), <i>AE</i> only includes additive genetics and unique environment, and <i>CE</i> only includes common and unique environment;</p>†<p>Proportion of variance (and 95% confidence interval) due to additive genetics, shared environment, and unique environment factors according to each model;</p>‡<p>Akaike's information criterion (AIC) is a global measure of goodness of fit, with the best-fitting and most parsimonious models shown in bold.</p

Select characteristics of twins from same-sex pairs enrolled in the University of Washington Twin Registry.

*<p>Indicates difference between monozygotic and dizygotic twin pairs at <i>P</i><0.05; data for cut-points presented as percentage achieving that standard; SD, standard deviation.</p

Within-pair tetrachoric correlations and 95% confidence intervals for each binary activity measure in monozygotic (solid white bars) and dizygotic (hatched bars) twins.

<p>Within-pair tetrachoric correlations and 95% confidence intervals for each binary activity measure in monozygotic (solid white bars) and dizygotic (hatched bars) twins.</p