Impact of illness scale: reliability, validity, and cross-cultural utility

We report on the development of a brief (nine-item) Impact of Illness Scale (IIS), which measures the degree that an illness is perceived to restrict psychosocial functioning. The measure is shown to have high internal consistency in a variety of samples. Its construct validity is indicated by correlations with other scales measuring general functioning in samples affected by illness. There is little variation in correlations between the IIS and other measures across a number of groups from different language and cultural backgrounds. This, together with the finding that items retain their psychometric properties when used to make general ratings of mental disorders, suggests that the content of the IIS is valid. The results suggest the IIS is a reliable and valid measure of psychosocial impact of illness that may be applicable in a wide range of sociocultural settings.