Introduction
Methods
Participants
Category | Sample 1 (%) | Sample 2 (%) | |
---|---|---|---|
Time 1 | Time 2 | ||
Gender | |||
Female | 140 (55.6%) | 101 (53.4%) | 366 (57.2%) |
Male | 110 (43.7%) | 88 (46.6%) | 267 (41.7%) |
Others | 2 (0.8%) | 0 (0.0%) | 7 (1.1%) |
Age | |||
18–20 | 2 (0.8%) | 1 (0.5%) | 97 (15.2%) |
21–30 | 42 (16.7%) | 30 (15.9%) | 134 (20.9%) |
31–40 | 95 (37.7%) | 64 (33.9%) | 138 (21.6%) |
41–50 | 85 (33.7%) | 70 (37.0%) | 139 (21.7%) |
51 or over | 28 (11.1%) | 24 (12.7%) | 132 (20.6%) |
Employment | |||
Full-time employment | 118 (46.8%) | 88 (46.6%) | 260 (40.6%) |
Unemployed | 75 (29.8%) | 52 (27.5%) | 167 (26.1%) |
Student | 7 (2.8%) | 6 (3.2%) | 94 (14.7%) |
Part-time employment | 47 (18.7%) | 38 (20.1%) | 114 (17.8%) |
Night worker | 5 (2.0%) | 5 (2.6%) | 5 (0.8%) |
Having trouble with BP | |||
Yes | – | – | 275 (43.0%) |
No | – | – | 365 (57.0%) |
Age | Full-time employment | Unemployed | Student | Part-time employment | Night worker |
---|---|---|---|---|---|
18–20 | 9 | 5 | 80 | 3 | 0 |
21–30 | 56 | 36 | 14 | 27 | 1 |
31–40 | 71 | 40 | 0 | 27 | 0 |
41–50 | 71 | 41 | 0 | 26 | 1 |
51– | 53 | 45 | 0 | 31 | 3 |
Questionnaires
Bedtime procrastination
General procrastination
Self-control
Insomnia symptoms
Sleep schedules
Procedures
Analysis
Preregistered analyses
Types of reliability and validity | Predicted results |
---|---|
Internal consistency | The α coefficient of the BPS is approximately .90 [5], and the Japanese version of the scale is expected to show similar high internal consistency(α≧.80) |
Factorial validity | By conducting an exploratory factor analysis in Sample 1 and a confirmatory factor analysis in Sample 2 based on the results of the exploratory factor analysis, a one-factor structure of the BPS is expected [5]. In the exploratory factor analysis, the result of the parallel analysis is used as the criterion for the number of factors In confirmatory factor analysis, CFI ≥ .95, TLI ≥ .95, RMSEA ≤ .06, and SRMR ≤ .08 are used as criteria for the validity of the one-factor structure in terms of model fit |
Construct validity | Consistent with Kroese et al. (2014), we expect to find a moderate positive association between the BPS and general procrastination. A moderate (> = .30) negative association is noted between the BPS and self-control, sleep quantity, and sleep quality |
Test–retest reliability | Consistent with Kroese et al.’s study (2016) (r = .79), a good retest reliability (between .75 and .90) is expected |
Criterion-related validity | Since the BPS includes questions about the frequency of delayed bedtime, the group with a higher predisposition to delayed bedtime had significantly higher BPS scores than the group that did not |
Exploratory analysis
Results
Validation of the Japanese version of the BPS
Factorial validity
Kaiser–Meyer–Olkin MSA | Factor loadings (SD) | ||
---|---|---|---|
Sample 1 (Time1) | Sample 2 | Sample 2 | |
BPS 1 | .92 | .92 | .90 (.04) |
BPS 2 | .45 | .72 | .12 (.04)a |
BPS 3 | .95 | .93 | .79 (.05) |
BPS 4 | .92 | .93 | .96 (.04) |
BPS 5 | .94 | .93 | .82 (.04) |
BPS 6 | .90 | .91 | .89 (.03) |
BPS 7 | .94 | .92 | .90 (.04) |
BPS 8 | .96 | .96 | .78 (.04) |
BPS 9 | .94 | .94 | .86 (.04) |
Internal consistency
Test–retest reliability
Construct validity
Variable | Mean (SD) | Correlation with BP |
---|---|---|
BPS | 26.71 (7.50) | – |
General procrastination | 28.15 (10.21) | .47* |
Self-control | 39.46 (9.08) | – .41* |
AIS | 6.52 (4.21) | .44* |
Sleep onset latency (weekdays; minutes) | 57.00 (137.40) | – .03 |
Sleep onset latency (holidays; minutes) | 61.80 (142.20) | – .02 |
Sleep hours (weekdays) | 6.44 (1.20) | – .26* |
Sleep hours (holidays) | 7.22 (1.40) | – .08 |
Sleep efficiency (weekdays) | 0.89 (0.12) | – .14* |
Sleep efficiency (holidays) | 0.90 (0.18) | – .08* |