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    • Statistical comparisons between PSG and actigraphy measures

    2018-10-26

    Statistical comparisons between PSG and actigraphy measures obtained from either the original or spline-modified data were performed using several methods: (1) Sleep summary measures obtained from the wrist and hip actigraphy recordings were compared with mean PSG values using a nonparametric Wilcoxon rank sum test applied to differences. (2) Associations of PSG with actigraphy summary data were further assessed using Spearman correlations. (3) Minute-by-minute agreement of PSG with actigraphy was determined by serially evaluating concordant or discordant epochs of PSG and actigraphy. The total number of concordant epochs were divided by TIB then multiplied by 100 to obtain the percent agreement and then averaged among all subjects. (4) Sensitivity of actigraphy scoring was calculated for each participant as the percent of PSG-scored sleep epochs that also were scored as sleep by the actigraph; specificity was calculated as the percentage of PSG-scored wake epochs that also were scored as “awake” by the MTI software. Individual sensitivity and specificity data were then averaged across all subjects. (5) Bland–Altman plots were used to provide a visual summary of the agreement between PSG and other sleep summary measures. These graphs were generated by plotting the mean of the two sleep measures (e.g., spline-modified sleep efficiency and PSG sleep efficiency) against the difference between the actigraphy and referent (PSG) sleep efficiencies, along with the 95% limit of agreement for the mean differences, and the intraclass correlation coefficient (ICC) (BA.plot function, R MethComp package, http://cran.r-project.org/web/packages/MethComp/MethComp.pdf). All analyses were performed using the R Gui© software program (The R Foundation for Statistical Computing). The statistical significance level was set at α=0.05.
    Results Analyses were performed among the 54 qualified participants who had at least 6h of PSG sleep and data from both actigraph monitors (54/84; 64%). The average age (± standard deviation) of the study buy buspirone hcl was 51±13 years, including 29 (54%) women, 20 men (37%) for whom sex data were recorded. Subjects were given a presumptive diagnosis based on their initial assessment and self-reported symptoms which may or may not have been consistent with their final diagnosis. Many patients reported more than one symptom (e.g., insomnia or hypersomnia with sleep apnea). Based on their presumptive diagnosis, the sample consisted of 32 patients with primary symptoms of obstructive sleep apnea, 11 with insomnia, 1 with narcolepsy, and 10 normal or undiagnosed sleepers. Table 1 summarizes demographic characteristics of the participants. Fig. 1 presents an example of the spline-modified wrist actigraphy data (lower panel) relative to the original (middle panel) and PSG-defined sleep and wake (upper panel) for a participant׳s single night sleep record (An example of hip actigraphy data is presented in the supplemental appendix Fig. S1.) The estimated overall adjusting magnitude and penalty parameter that minimized the sleep efficiency between actigraphy and PSG for the wrist data was 300 and 0.00025, respectively, and for the hip data 400 and 0.00025, respectively. Note that in this example, wakefulness (white background) for the spline-modified sleep scoring procedure coincides more consistently with PSG sleep–wake scores relative to the original actigraphy data, and that sleep efficiency using spline-modified values more closely approximates PSG sleep efficiency. Sleep summary measures for PSG, original wrist and hip actigraphy, and spline-modified wrist and hip actigraphy data are presented in Table 2. Compared to the statistics using spline-modified data, summary statistics based on original wrist actigraphy data were farther from the statistics for PSG. The spline-modified wrist actigraphy means for buy buspirone hcl sleep efficiency, TST, WASO, and number of awakenings were not statistically different from PSG data. The spline-modified latency was statistically lower (p<0.001) than the PSG data, but it is still closer to the PSG value than if not modified. The mean spline-modified hip actigraphy data corresponded more closely with PSG than the original hip data, although the summary measures were statistically different from the PSG measures (all p<0.01, Table 2).