Table 2.

Definition of sleep groups

Groups	Sample	Defining criteria
1 (≤6 h) and 3 (7–8 h)	Lifebrain/HCP	Yes to all of the following: (1) Usual sleep latency (PSQI2) < 30 min (2) Less than once a week (PSQI5a): sleep latency > 30 min (3) Less than once a week (PSQI5b): nightly or early morning awakenings (4) Less than once a week (PSQI8): trouble staying awake during daytime
1 (≤6 h) and 3 (7–8 h)	UKB	Responses to all the following: (1) “Very easy/fairly easy” (field 1170): trouble getting up (2) “Never/rarely” (field 1190): nap during day (3) “Never/rarely” (field 1200): sleeplessness (4) “Never/rarely” (field 1220): daytime dozing
2 (≤6 h) and 4 (7–8 h)	Lifebrain/HCP	Yes on at least two of the following: (1) Usual sleep latency (PSQI2) > 30 min (2) More than once a week (PSQI5a): sleep latency > 30 min (3) More than once a week (PSQI5b): nightly or early morning awakenings (4) More than once a week (PSQI8): trouble staying awake during daytime
2 (≤6 h) and 3 (7–8 h)	UKB	Responses to all the following: (1) “Not very easy/not at all easy” (field 1170): trouble getting up (2) “Sometimes/usually” (field 1190): nap during day (3) “Sometimes/usually” (field 1200): sleeplessness (4) “Sometimes/often” (field 1220): daytime dozing

The PSQI response category “Less than once a week” here also includes the response “Not during the past month.”