Table 2.
Mean BMI change from baseline (1993) to follow-up (1997) associated with baseline BMI, baseline BMI squared, and job strain exposure patterns.
| Independent variable | Model 1 | Model 2 | ||||
|---|---|---|---|---|---|---|
|
| ||||||
| ΔBMI | (95% CI) | p-value | ΔBMI | (95% CI) | p-value | |
| Baseline BMI (mean-centered) | 0.032 | (0.027, 0.038) | <0.0001 | 0.031 | (0.025, 0.036) | <.0001 |
| Baseline BMI (mean-centered) squared | −0.007 | (−0.007, −0.006) | <0.0001 | −0.007 | (−0.007, −0.006) | <.0001 |
| Job strain exposure at baseline and follow-upa | <0.001b | 0.002b | ||||
| Remained low (ref.) | 0.000 | -- | 0.000 | -- | ||
| Decreased | 0.073 | (0.017, 0.129) | 0.011 | 0.063 | (0.006, 0.120) | 0.030 |
| Increased | 0.077 | (0.013, 0.141) | 0.019 | 0.074 | (0.009, 0.138) | 0.025 |
| Remained high | 0.125 | (0.052, 0.199) | <0.001 | 0.118 | (0.044, 0.193) | 0.002 |
| Baseline BMI*job strain exposure | 0.016b | 0.015b | ||||
| Baseline BMI*Remained low (ref.) | 0.000 | -- | 0.000 | -- | ||
| Baseline BMI*Decreased | 0.001 | (−0.009, 0.012) | 0.820 | 0.001 | (−0.009, 0.011) | 0.843 |
| Baseline BMI*Increased | −0.000 | (−0.012, 0.011) | 0.977 | 0.000 | (−0.011, 0.012) | 0.975 |
| Baseline BMI*Remained high | 0.021 | (0.008, 0.034) | 0.001 | 0.022 | (0.008, 0.035) | 0.001 |
Notes. Baseline BMI was mean-centered, and the square term was calculated with the centered value. Model 1is adjusted for baseline age, race/ethnicity, the number of pregnancies up to baseline, and the number of pregnancies between baseline and follow-up. Model 2 includes the following baseline covariates in addition to what is in Model 1: type of job at baseline and follow-up, average sleep duration, smoking status, the number of cigarettes per day, diet, physical activity, and average time spent on watching TV.
Because the interaction term is included in the models, the main effect results should be interpreted only when baseline BMI (mean-centered)=0; that is, the main effects of job strain exposure are for women whose baseline BMI was the average value (=25.2). For all others, the effect of job strain exposure depends on the baseline BMI.
p-value for the likelihood ratio test with df=3