Dependent Variable (For Models I-IV) | Independent Variables and Models |
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Model I: ISI 7 items $Utilit{y}_{\phantom{\rule{0.2em}{0ex}}mod\phantom{\rule{0.2em}{0ex}}elI}=1-exp\left(\alpha +\sum _{j=0}^{7}{X}_{i}{\beta}_{ij}\right)$ Where $\sum _{j=0}^{0}{X}_{i}{\beta}_{i0}\equiv 0$and, i = 1,...,7 representing 7 ISI items, j = 0,...,4, representing 5 levels of the Likert scale. | |
Model II: ISI summary scores (0-28) $Utilit{y}_{ModelII}=1-exp\left(\alpha +X\beta \right)$ Where X is the ISI summary scores range from 0(min) to 28 (max) and treated as a continuous variable in the model | |
EQ-5D disutility values $Disutility=exp\left(\alpha +\sum X\beta \right)$ Utility = 1-Disutility |
Model III: ISI 4 clinical categories $Utilit{y}_{ModelIII}=1-exp\left(\alpha +\sum _{j=1}^{4}X{\beta}_{ij}\right)$ Where $\sum _{j=1}^{1}{X}_{i}{\beta}_{i1}\equiv 0$and, j = 1,...,4 representing 4 clinical classifications based on insomnia summary scores. |
Model IV: Insomnia symptoms and demographics $Utilit{y}_{ModelIV}=1-exp\left(\alpha +\sum _{i=1}^{8}{X}_{i}{\beta}_{i}+{X}_{duratio{n}^{2}}^{2}{\beta}_{duratio{n}^{2}}\right)$ Where i = 1,...,8 representing 5 symptoms, 2 demographic variables and 1 variable indicating the presence/absence of comorbidity. The 5 symptom variables were: sleep duration, quality, latency, next day sleepiness, and number of wakeup times during the night. The 2 demographic variables were age and gender. Within the model, a sleep duration squared term was an additional predictor adjusting the concave function of sleep duration on health state utilities. |