Psychometric properties of the Impact of Event Scale amongst women at increased risk for hereditary breast cancer.

The Impact of Event Scale (IES; Horowitz MJ, Wilner N, Alvarez W. 1979. Psychosom Med 41: 209-218) has been widely used in the psycho-oncology literature as a measure of cancer-related anxiety. More recently, the IES has been applied to the assessment of breast cancer-related anxiety amongst women who are at increased risk of developing hereditary breast cancer. Despite its widespread use, no studies to date have described the validity of the IES amongst these women. The present study is a replication of reliability analyses and exploration of the factor structure and validity of the IES amongst a sample of 480 female hereditary breast cancer clinic patients. Results suggest good internal consistency (Cronbach's alpha=0.84-0.91), and satisfactory test-retest reliability (IES-Total r=0.80). The IES was found to have good face validity and be an acceptable instrument to women at increased risk of breast cancer. The two-factor (intrusion and avoidance) structure originally reported (Horowitz et al. 1979; Zilberg NJ, Weiss DS, Horowitz MJ. 1982. J Consult Clin Psychol 50: 407-414) was replicated by factor analysis in the present study. Analysis of correlation coefficients between the IES, breast cancer-related events and attitudes and other standardized measures of distress and general somatic concern, provide some preliminary support for the concurrent and discriminative validity of the IES amongst women at increased risk of developing hereditary breast cancer. Copyright 2001 John Wiley & Sons, Ltd.