Of 8,000 potential participants mailed invitation letters, 442 were found to be ineligible (due to having died or no longer having GHC health plan coverage). Of the remaining 7558 eligible women, 865 could not be reached by telephone and 2033 declined to participate, resulting in 4660 women (62% of those eligible) who completed a telephone survey. Data from an additional five women were excluded due to outlying height or weight variables that could not be verified for accuracy. Available data on nonresponders indicate that, compared to those who completed a survey, women who declined participation or who could not be reached were younger [51.8 vs. 52.4 years, t(7998) = -4.06, p < 0.0001] and had lower average BMI [33.3 vs. 34.0 kg/m2, t(5532) = -3.95, p < 0.0001].
Among those who completed a survey, sample weighted mean age was 52.1 years, sample weighted mean BMI was 28.3 kg/m2 (standard error = 0.11; 95% confidence interval = 28.11-28.54; range = 15.81-74.88), 65.8% were married, 66.5% had completed at least 2 years of college, and 70.0% were employed. Nearly 4% were of Hispanic origin, and 82.4% were white. Thirty-seven percent reported never weighing themselves, 27% reported weighing themselves monthly, 24% reported weighing themselves weekly, and 12% reported weighing themselves daily. Weighted prevalence of current major depression was 5.1%; an additional 7.8% had a PHQ score greater than 10, suggesting moderate symptoms.
presents mean BMI values by depression and self-weighing frequency categories; values are adjusted to reflect sampling weights. Results of weighted chi-square analyses [χ2(6) = 27.72, p < 0.05] and the unadjusted correlation between depression status and self-weighing (r = -0.04, p < 0.01) were statistically significant (see ). The association between depression and self-weighing was no longer statistically significant after adjusting for BMI [Wald χ2(3) = 6.82, p > 0.05); r = -0.02, p > 0.10].
Body mass index (kilograms/meters2) by depression and self-weighing frequency categories among women ages 40-65 surveyed in Seattle, Washington from November 2003-February 2005.
Figure 1 Percent of sample in each weighing frequency category by depression status category. Sample sizes are adjusted to reflect sampling weights. PHQ = Patient Health Questionnaire; a score > 10 indicates the presence of moderate depressive symptoms. (more ...)
Associations of Depression and Self-Weighing Frequency with BMI
An initial regression of depression, self-weighing frequency, and their interaction on BMI was examined; no other covariates were considered in this initial model. Depression was positively related and self-weighing frequency was negatively related to BMI [F(2, 4,590) = 39.53 and F(3, 4,590) = 7.16, p < 0.0001]; however, the depression by self-weighing interaction term was not statistically significant [F(6, 4,590) = 0.73, p = 0.63]. Thus, only main effects were considered further in a weighted regression model examining the associations of depression and self-weighing frequency on BMI.
Results of the regression of depression status (three categories, as presented in ) and self-weighing frequency (four categories, as presented in ) on BMI, adjusting for demographic factors (age, marital status, education level, race/ethnicity, employment status, smoking history, current smoking) are presented in Tables and . The overall model was statistically significant [F(14, 4,578) = 19.63, p < 0.0001] and accounted for 10.2% of the variance in BMI. After adjustment for demographic variables, the absence of depression [F(2, 4,578) = 29.78, p < 0.0001] and greater self-weighing frequency [F(3, 4,578) = 6.95, p = 0.0001] were independently associated with lower BMI; results are comparable with those from the initial unadjusted model noted above. Comparisons of weighted, adjusted means presented in suggest that daily weighing frequency, more so than weekly or monthly frequency, and the absence of depressive symptoms (compared to those with PHQ > 10 or those with major depression) are associated with lower average BMI.
Weighted regression of depression and self-weighing frequency on body mass index (kilograms/meters2) among women ages 40-65 surveyed in Seattle, Washington from November 2003-February 2005.
Mean adjusted body mass index (kilograms/meters2) by depression status and weighing frequency among women ages 40-65 surveyed in Seattle, Washington from November 2003-February 2005.