OC, depressive and insomnia symptoms in adult women with and without depression 49 contraceptives and reported a regular menstrual cycle were clustered in the NC observations (this included women who reported using a copper IUD or condoms for contraception), resulting in a total of 1913 observations. Observations in women who reported using OC at time of the measurement were clustered in the OC group, resulting in 1301 observations. This enabled a cross-sectional comparison of measurements based on contraceptive status (either during OC use or during non-OC use) within the longitudinal NESDA study setup. Figure 2.1B shows the sample sizes of both contraceptive status groups and sample sizes over time, including the breakdown of group size. This process resulted in a total sample of 1205 women who contributed 3214 observations (mean number of observations per woman=2.7). 2.3. Depressive disorders, and symptoms of depression and insomnia To assess the presence of MDD or dysthymia (as defined by DSM-IV, American Psychiatric Association, 1994) the Composite International Diagnostic Interview (CIDI, version 2.1; Nelson, 1999) was used. This means that the knowledge on all current and previous diagnoses in this study was acquired using clinically validated methods. The CIDI was conducted at every assessment by trained research staff. Diagnoses of MDD and dysthymia within the last 6 months were used as an outcome measure for current depressive or dysthymic disorder. To assess the severity of depressive symptoms, all participants filled out the well-validated Self Rated Inventory of Depressive Symptomatology (IDS-SR) at every assessment wave. The IDS-SR has excellent internal consistency (Cronbach’s alpha=0.94, Rush et al., 1996). The items in the IDS-SR are scaled on a Likert scale from 0 to 3 with 0 meaning the symptom is not present, and 3 meaning high symptom severity. The IDS-SR has 30 items, of which the scores of individual items can be summed to form a sum score that represents the depressive symptom severity. Sub-scores for atypical depression were calculated based on characteristics of atypical depression according to the DSM-IV by calculating the sum of item scores for hypersomnia (item 4), mood reactivity (item 8, reverse scored to represent absence of anhedonia), increased appetite (item 12), weight gain (item 14),
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