Measuring the error in sleep estimation in normal subjects and in patients with insomnia.

The aims of this study were to measure the error in sleep estimation in normal controls and subjects with primary insomnia to establish the minimum amount of sleep needed for reliable subjective estimation and to depict the distribution of the error in sleep estimation in both groups. A two-step retrospective (study 1) and prospective (study 2) validation study was carried out. Study 1 included 288 normal subjects [176 females and 112 males, mean age 58.