Survival curves for patients prescribed no hypnotic
are compared with survival curves for patients prescribed
hypnotics, divided into four age groups (age at commencement
of period of observation). These curves were derived from
a special Cox proportional hazards model in which those taking
and not taking hypnotics in the four age groups were coded as
eight categories of an independent predictor variable. The
curves represent the fraction of patients surviving over the
increasing years of observation until censored (died, lost to
follow-up or end of observation). Those censored <0.23 year
of observation were excluded. The red curves represent the
fact that a higher percentage of hypnotic users died during the
observation periods and fewer survived. Each curve was
adjusted for covariates except age (which shared excessive
colinearity with the age-based categories) and was adjusted for
comorbidity strata.
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http://bmjopen.bmj.com/content/2/1/e000850.full
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