Method: A total of 53 adults (mean age 37.13 ± 12.16 yrs) completed the SBR for 7 consecutive days. Each participant’s data were screen for errors or missing days. One participant was excluded from analysis due to missing data. The remaining 52 participants were analyzed using the Generalizability Theory. A single-facet crossed design [i.e., Participant (P) x Days (D)] was used. Outcome measurements were SBR with sleep time included (SBR-S) and SBR without sleep time (SBR-NS). G-studies were performed to quantify the percentage of variance associated with the facet and interaction in the model. Follow-up D-studies were performed to determine the minimum number of days of SBR data collection needed to achieve a desirable reliability coefficient (G ≥ .80).
Analysis/Results: The average daily SB minutes of SBR-S and SBR-NS were 1041.61 ± 172.62 and 547.82 ± 161.27 min/day, respectively. The results from the G-studies show that for both SBR-S and SBR-NS, P accounted for 45% and 51% of the variance, while D had little effect on the total variance with 1% and 2%, respectively. A relatively large portion of variance was unidentified (i.e., the P x D interaction). The number of days to achieve G ≥ .80 for SBR-S and SBR-NS was 5 and 4 days, respectively.
Conclusions: The minimum number of days necessary to achieve a reliability coefficient (G ≥ .80) ranged from 5 or 4 days whether sleep time was included or excluded. The SBR is an inexpensive method for estimating SB minutes in large samples of adult populations. When conducting studies to measure SB time, researchers need to consider the minimum number of days required to ensure reliable estimates of SB.
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