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Fig. 1. Kaplan-Meier survival curves. a, Survival as a function of sleep latency (log-rank test = 9.63, p = .002). b, Survival as a function of sleep efficiency (log-rank test = 11.60, p = .0007). c, Survival as a function of percentage of REM sleep (log-rank test = 6.58, p = .010). df = 1 for all tests. Mean survival times (in weeks) were 614 and 752 for greater and lesser sleep latency, respectively; 624 and 754 for lesser and greater sleep efficiency, respectively; and 608 and 751 for extreme percentage of REM sleep and less extreme percentage of REM sleep. + = censored observation.
