Cortisol dynamics and sleep quality: the role of sex and oral contraceptive use 109 2.3. Outcome variables Cortisol sampling Cortisol samples were collected using Salivette® tubes (Sarstedt, Neubringen, Germany), and participants were asked to chew on the swab in the Salivette® tube until it was saturated. Participants were instructed to avoid physical exercise, eating, drinking, brushing their teeth and smoking before and during the morning hour of saliva sampling. For the measurement of the CAR, participants collected saliva at five time points: immediately after awakening, and 15, 30, 45 and 60 minutes after awakening. Participants also noted whether the date of collection was a work day, study day, or day off and the specific times at which each sample was taken. After sample collection, the samples were kept at 5 degrees Celsius (fridge) and then returned to the laboratory for analysis. Full details of the CAR sampling methods are described in (Nasser et al., 2023). The baseline cortisol measurement was defined as the absolute cortisol level after waking, and the CAR was determined as the area under the curve with respect to increase from baseline (AUCi). Since the CAR AUCi is the calculation of the increase in cortisol with respect to baseline, it is considered an index of the HPA dynamics. Sleep outcomes Both outcome variables, i.e. sleep quality and sleep disruption, were obtained using the PSQI. The PSQI is a self-report questionnaire inquiring about sleep in the last month. It consists of 7 components, including subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication and daytime dysfunction (Buysse et al., 1989). To assess total sleep quality, each component of the PSQI was scored on a scale of 0 to 3, resulting in a PSQI sum score between 0 and 21, with higher scores representing poorer sleep quality. A PSQI sum score higher than 5 indicates poor sleep quality. In order to replicate the findings in Morssinkhof et al. (2021), we aimed to select a measure for sleep disruptions which was as close as possible to the sleep disruption item in the original study (Women’s Health Initiative-Insomnia Rating Scale item 2: “Did you wake up several times at night?”, scored from 0: “No, not in the past 4 weeks” to 4: “Yes, 5 or more times a week”). To replicate this item as best as possible, we selected item 5B from the PSQI to
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