Chapter 2 54 measurement (see Figure 2.1B). A total of 612 women contributed only to NC measurements (a total of 1467 measurements), 327 women contributed only to OC measurements (a total of 803 measurements), and 266 women contributed both to OC and NC measurements (a total of 944 measurements). Participants were on average 35.6 (SD 9.0) years old, had received 13.5 years of education (SD 3.2), and 91.4% were born in the Netherlands. OC use was significantly associated with younger age compared to NC measurements, and measurements in OC users were more likely to be in participants born in the Netherlands, but level of education, partner status, or BMI did not differ between OC measurements and NC measurements. Means and percentages of sociodemographic variables are displayed in Table 2.1. Table 2.1. Description of the sociodemographic variables across measurements. Contraceptive status during measurement Naturally cycling Oral contraceptive use p-value # of observations 1913 1301 - Age in years (mean, SD) 38.1 (8.0) 31.9 (9.1) < 0.001 Highest education in years (mean, SD) 13.5 (3.2) 13.4 (3.2) 0.48 BMI in kg/m2 (mean, SD) 25.1 (5.2) 24.7 (5.2) 0.054 Born in the Netherlands (n, %) 1703 (89.0) 1234 (94.8) < 0.001 Has a partner (n, %) 1376 (71.9) 942 (72.8) 0.62 Depression status (n, %) No MDD or dysthymia 433 (22.6) 268 (20.6) 0.22 Remitted from MDD or dysthymia 920 (48.1) 664 (51.0) Current MDD or dysthymia 560 (29.3) 369 (28.4) BMI=Body Mass Index, SD=standard deviation. p-values obtained from independent samples ttest or from chi-square test for cross-tabulation. 3.2. Current oral contraceptive status and depression We observed a statistically significant difference in the IDS-SR scores between OC and NC measurements of 0.90 points (95% CI=(0.00, 1.80); p=0.049; Table 2.2), although this difference was small in terms of effect size (Cohen’s d=0.07) due to large differences within the groups, resulting in a high SD. This difference in IDS-SR scores was no longer significant after adjustment for the demographic covariates (B=0.10, 95% CI=(-0.80, 1.00),
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