Preliminary validation of the insomnia severity index in Danish outpatients with a medical condition.

Purpose: Insomnia is a frequent sleeping disorder in the general and clinical population. With an increasing proportion of health care services being provided as outpatient care, a short, valid and reliable tool is needed to identify insomnia in medical patients under outpatient care in Denmark. The Insomnia Severity Index (ISI) could be the needed tool if found valid and reliable.