Lail et al. BMC Public Health 2011, 11:148 http://www.biomedcentral.com/1471-2458/11/148 Page 3 of 7 Figure 1 Summary of the sampling method and respondent participation. Respondents living in a household with dogs were coded as dog-owners, as opposed to non-owners. Those that changed their dog-ownership status between the two surveys were not included in the analysis (n = 10). Statistical Analysis All baseline demographic characteristics were compared for dog-owners and non-owners using Pearson’s chi- square for categorical variables and independent t-tests for continuous variables. The absolute difference in min- utes of NTW and NRW was also calculated (i.e., winter minus summer minutes) with positive values represent- ing more weekly walking in winter compared with sum- mer, and negative values representing less weekly walking in winter compared with summer. A general lin- ear model was used to regress the difference in minutes of NTW and NRW between winter and summer onto dog-ownership status while adjusting for demographic characteristics. To aid with interpretation, estimates asso- ciated with dog-ownership status are presented as mar- ginal (i.e., adjusted) means. To examine whether or not dog-owners and non-own- ers participation in neighbourhood walking remained stable from winter to summer, respondents were coded into four categories: 1) consistent participators: any walking in both winter and summer; 2) consistent non- participators: no walking in either winter or summer; 3) summer-only participators: some walking in summer, but not in winter; and 4) winter-only participators: some walking in winter, but not in summer. Logistic regres- sion odds ratios (OR) and 95% confidence intervals (95%CI) were used to estimate the association between dog-owner status and stability of participation (or non- participation) in neighbourhood-based walking for trans- portation (NTW) and for recreational (NRW) from summer to winter, adjusting for demographic character- istics. Stata 10.1 statistical software was used for all analyses. Results The average age of the sample (n = 428) was 53 ± 15 years. The sample included 115 dog-owners (26.9%) and 313 non-owners (73.1%). While dog-owners were dispro- portionately white, higher-income, residing in a detached or semi-detached house, there was no difference between dog-owners and non-owners in education, marital status or sex (Table 1). In the summer, dog-owners on average spent 213.6 min/week in NRW, compared with non-owners who spent on average 123.3 min/week (Table 2). Meanwhile, in the winter, dog-owners on average spent 253.2 min/ week in NRW compared with non-owners who spent 107.1 min/week. Less time per week was spent in NTW than in NRW among dog-owners and non-owners (Table 2). Weekly minutes of NTW were not significantly differ- ent between dog-owners and non-owners, for either sum- mer or winter. Adjusting for demographic characteristics, there was no statistically significant difference in the change in weekly NTW minutes from winter to summer between dog-owners and non-owners (Table 2). We did, however, find that dog-owners undertook on average 39.6 min/week more NWR in winter than in summer, while non-owners undertook 16.2 min/week less NWR in winter than in summer (Table. 2). This result suggests a difference between dog-owners and non-owners in weekly NWR minutes across seasons - even after adjust- ing for demographic characteristics. Among all respondents, 65.1% participated in NRW in both winter and summer, 8.9% participated in NRW in the summer only, 10.5% participated in NRW in the win- ter only, and 15.4% did not report any participation in