(e.g., excessive caffeine use,  irregular sleep schedules).
Gender-Related Diagnostic Issues
Insomnia is a more prevalent complaint among females than among males, with first onset
often associated with the birth of a new child or with menopause. Despite higher preva-
lence among older females, polysomnographic studies su ggest better preservation of
sleep continuity and slow-wave sleep in  older females than in older males.
Diagnostic Markers
Polysomnography usually shows impairments of sleep continuity (e.g., increased sleep la-
tency and time awake after sleep onset and de creased sleep efficiency [percentage of time
in bed asleep] and may show increased stage 1 sleep and decreased stages 3 and 4 sleep.
The severity of these sleep im pairments does not always ma tch the individual’s clinical
presentation or subjective complaint of poor sleep, as individuals with insomnia often un-
derestimate sleep duration and overestimate wakefulness relative to polysomnography.
Quantitative electroencephalographic analyses  may indicate that individuals with insom-
nia have greater high-frequency electroencepha lography power relative to good sleepers
both around the sleep onset period and duri ng non–rapid eye movement sleep, a feature
suggestive of increased cortical arousal. Individual s with insomnia disorder may have a
lower sleep propensity and typically do not show increased daytime sleepiness on objec-
tive sleep laboratory measures compared wi th individuals without sleep disorders. 
Other laboratory measures show evidence, although not consistently, of increased
arousal and a generalized activation of the hypothalamic-pituitary-adrenal axis (e.g., in-
creased cortisol levels, heart rate  variability, reactivity to stre ss, metabolic rate). In general,
findings are consistent with the hypothesis that increased physiological and cognitive
arousal plays a significant role in insomnia disorder.