As the name implies, the Insomnia Impact Scale (IIS) assesses the impact of poor sleep on wakeful functioning. The IIS was developed by Hoelscher, Ware, and Bond in the early 1990s. The scale is based on a self-report questionnaire that measures the level of agreement, one through five, to a series of 40 statements. These statements cover physical, cognitive, emotional, social, and occupational aspects of poor sleep. Based on the overall scores (ranging between 40 and 200) and scores within subject areas, IIS administrators were able to discriminate between people with insomnia that presented at a sleep disorder center and self-reported normal sleepers. Based on a review of PubMed, the IIS does not appear to be widely used in published research studies since the phrase “Insomnia Impact Scale” does not return any exact results. Upon further investigation, the IIS appears to have been used in less than ten studies since its initial publication and validation. One limitation of the IIS is that the scale does not have published norms which to compare. Researchers have used a score of 125 and above as indicative of significant disruption in daytime functioning.
Spanish psychiatrists recently developed what they call the insomnia Diurnal Impact Scale (IDIS) It uses six “items”. We don’t know what they mean by items, but presumably these are subjective questions for the patients.
The doctors say their scale has internal consistency ( http://www.ncbi.nlm.nih.gov/pubmed/21640386) – which is important in establishing the validity of any test – and can usually distinguish insomniacs from non-insomniacs. Like the IIS, the IDIS is intended to measure the impact of insomnia on waking life.
Insomnia Severity Index
An Insomnia Severity Index was developed by Canadian scientists and it has been validated by correlation with information from sleep diaries and polysomnography.
The Insomnia Severity Index is a seven-question test where the patient self-evaluates his or her own experience of insomnia on a 5-point scale. Your clinician may ask you to take it, although we have not found that it is in widespread use. Nurses and doctors may have their own formal or informal scales.