Variable Details
Sleep quality
Sleep quality, global (Modified PSQI)
Sleep quality is measured using a modified version of the Pittsburgh Sleep Quality Index (PSQI) and items from the Berlin questionnaire.
The individual items are used to calculate scores for the following components: sleep latency, sleep duration, sleep efficiency, sleep disturbances, sleeping medication use, and daytime dysfunction. The total score for sleep quality ranges from 0 to 16 and is the sum of all six component scores.
Sleep latency:
During the past month, how long (in minutes) has it usually taken you to fall asleep each night? [0 = 0 -15 minutes, 1 = > 15 minutes to 30 minutes, 2 = >30 minutes to 60 minutes, 3 = >60 minutes]
During the past month, how often did you have trouble falling asleep within 30 minutes? [0 = Not at all, 1 = less than once a week, 2 = Once or twice a week, 3 = Three or more times a week or nearly every day]
Sleep latency is the sum of the two items:
| Value | Sum of items |
|---|---|
| 0 | 0 |
| 1 | 1-2 |
| 2 | 3-4 |
| 3 | 5-6 |
Sleep duration:
In the past month, how many hours do you usually sleep at night?
| Value | Coding |
|---|---|
| 0 | ≥7 hours |
| 1 | 6 hours |
| 2 | 5 hours |
| 3 | 0 to <5 hours |
Sleep efficiency:
Sleep duration is converted to hours: During the past month, what time have you usually gone to bed at night? During the past month, what time have you usually gotten up in the morning?
Actual sleep time (hours): During the past month, how many hours of actual sleep did you get at night? (This may be different than the number of hours you spent in bed.)
Sleep efficiency = (actual sleep time/sleep duration)*100
| Value | Coding |
|---|---|
| 0 | >85 hours |
| 1 | >75 to 85 |
| 2 | >65 to 75 |
| 3 | ≤65 |
Sleep disturbance:
If question 2 is answered in the affirmative, question 3 is asked. Response values are recoded 0 to 3. Sleep disturbance is the mean of items 1 and 3.
- During the past month, how often did you wake up in the middle of the night or early morning? (See below)
- Do you snore? [Yes, No]
- Over the past month, how often have you been snoring? (See below)
| Value | Response value | Coding |
|---|---|---|
| 0 | 1 | Not at all |
| 1 | 2 | Less than once a week |
| 2 | 3 | Once or twice a week |
| 3 | 4 | Three or more times a week |
| 3 | 5 | Nearly every day |
Sleeping medication use:
Medication use is based on a detailed history of all medications consumed and examination of medication bottles. Participants are considered to be taking medications to help them sleep if they took any of the MediSpan coded insomnia medications in the preceding 2 weeks.
| Value | Coding |
|---|---|
| 0 | Absent |
| 1 | Present |
Daytime dysfunction: This component is scored using items from the Berlin questionnaire (rather than items 8 and 9 from the PSQI). Question 3 is asked if question 2 is answered in the affirmative. Response values are recoded 0-3. This variable is the sum of items 1 and 3, collapsed into 4 levels.
- How often do you get so sleepy during the day or evening that you have to take a nap? (See below)
- Have you ever nodded off or fallen asleep while driving a vehicle? [Yes, No]
- Over the past month, how often has this (nodded off or fallen asleep while driving a vehicle) occurred? (See below)
Item responses:
| Recoded value | Response value | Item 1 | Item 3 |
|---|---|---|---|
| 0 | 1 | Never | Not at all |
| 1 | 2 | Rarely | Less than once a week |
| 2 | 3 | Sometimes | Once or twice a week |
| 3 | 4 | Often | Three or more times a week |
| 3 | 5 | Very often | Nearly every day |
Daytime dysfunction:
| Value | Sum of items |
|---|---|
| 0 | 0 |
| 1 | 1-2 |
| 2 | 3-4 |
| 3 | 5-6 |