Once a week the participant completed 13 items of the depression subscale of the Symptom Checklist Revised (item labels start with SCL-90-R; [ 4 ]). Each item is scored on a 5-point Likert scale, with 0 meaning that the participant wasn’t bothered by that specific thought or feeling at all, and 4 meaning that he was extremely bothered by it.

Two separate sets of items were completed daily: a six-item set after waking up (item labels start with ‘mor’), with which information is collected on the quality of sleep. The other set consists of six items and were asked to be filled out right before the participant went to sleep (item labels start with ‘evn’). This set of items was concerned with the quality of the day the participant had. At both occasions, the participant was asked whether or not he took his medication either yesterday (morning item), or today (evening item). Three of the morning items were categorized accordingly. Two of the morning items and four of the evening items were measured on a 7-point Likert scale, ranging from 1 (not) to 7 (very). The medication items together with one evening item was measured dichotomously (yes/no).

33 items were measured on a 7-point Likert scale, ranging from 1 (not) to 7 (very). The items concerned with feeling down, lonely, anxious and guilty were measured on a 7-point Likert scale, ranging from –3 (not) to 3 (very). This scale differs from the majority of the items as a pilot trial showed that the participant reported more variation with a 7-point Likert scale ranging from –3 to 3 than a 7-point Likert scale ranging from 1 to 7. Items with respect to the company the participant was in, the activity the participant was enrolled in or any event that had taken place since the last assessment were categorized accordingly. Two items concerning the pleasantness and importance of the event were measured on a 7-point Bipolar scale, ranging from –3 (unpleasant/unimportant) to 3 (pleasant/important).

Momentary items (no. items is 50) were collected using the experience sampling method (ESM; [ 3 ]). Items were selected based on previous experience with these types of items regarding within-person variation, loading on a negative or positive affect component, the relevance for the current type of psychopathology and specific personal characteristics of the participant. The momentary assessment questionnaire consisted of items pertaining to mood states (e.g. feeling relaxed, feeling irritated etc.), self-esteem, the company the participant was in at the moment of assessment, the pleasantness or unpleasantness of being in company, physical condition, the activity that the participant was doing at the moment of assessment, and to an important event that had occurred since the last assessment.

The study lasted for 34 weeks. During this period, depressive symptoms were measured on a weekly basis. This weekly questionnaire was completed 28 times (= 82.4%). On each of these occasions, all items were answered.

During the entire study, 59.7% of the set of morning items and 81.5% of the set of evening items were completed. Each day, either the entire set of morning/evening items was answered, or none. On average, 3.6 (SD = 2.9) of the morning items and 4.9 (SD = 2.3) of the evening items were completed.

Each day, 43.4 items were filled out on average (SD = 1.3) per day at each assessment. In total, out of 1478 assessments, only five were aborted before completion. At 1478 assessments, items were completed on average 1280.4 times (SD = 378). Supplement “MissingnessMomentaryItems.pdf” gives a more detailed description of the missingness per assessment, day and item.

Procedures

The entire study comprised 5 phases: (1) a baseline measurement period that lasted four weeks, (2), a double-blind period in which the anti-depressant dosage was not yet reduced, which lasted between zero and six weeks, (3) a double-blind period in which the anti-depressant dosage was gradually reduced from 150 mg (venlafaxine) to 0 mg, which lasted eight weeks, (4), a post-assessment period in which the anti-depressant dosage was not changed, which lasted again eight weeks, and (5), a follow-up period that lasted twelve weeks.

The dose-reduction scheme issued in phase 3 was set up by the pharmacist who provided the anti-depressants during the study. Several reduction schemes were developed, which varied with respect to the length in weeks before the dose reduction started (phase 2). During the experiment, the participant and the researchers involved were unaware of the dose-reduction scheme, although they did know that the anti-depressant dosage was going to be reduced. The participant reported after the experiment that he had nog been able to figure out which eventual dose-reduction scheme had been used.

At the start of the experiment, the participant received a PsyMate (a digital device with touch screen, [5]), which was set up to send out a beep-signal at random moments within each of ten 90-minute intervals between 07.30 AM and 10.30 PM every day. At each beep-signal, the participant completed a 50-item questionnaire. Each beep-signal was accompanied by a ten-minute window in which the questionnaire was available to the participant. Assessments were started on average within 2.16 minutes (SD = 21 seconds). At the beginning and ending of each day, the participant was asked to complete an extra set of six items. On Mondays, the participant’s depressive symptoms were measured using the depression subscale of the SCL-90-R [4].