Behavioural response to illness: development and validation of a self-report measure of illness behaviour avoidance

A robust scale capable of assessing illness-related experiential avoidance (EA) in any given medical condition is currency lacking. Further, there is no available measure that assesses EA related to illness behaviours, i.e., actions and/or reactions in relation to feeling unwell that have the purpose of defining one’s state of health and obtaining physical or emotional relief from perceived or actual illness. This study intends to fill this significant gap by presenting the development and psychometric test of a measure of EA related to illness behaviour, the Illness Behaviour Avoidance Scale (IBAS). A total of 370 Portuguese adults with chronic illness participated in the study. The structure and validity of the IBAS was tested through an Exploratory Factor Analysis (EFA; n = 185), a Confirmatory Factor Analysis (CFA; n = 185), and reliability analyses. The IBAS presented a 7-item unifactorial structure, with good global (CMIN/DF = 2.08; CFI = 0.97; TLI = 0.94; SRMR = 0.04; RMSEA = 0.08, p = 0.139) and local adjustments (SRWs 0.56–0.73; SMCs 0.31–0.53). It also presented a good internal consistency (with αs = 0.82), and construct and discriminant validity. The IBAS appears to be a significant improvement from the use of previous EA measures in illness contexts. This scale can provide a measurement of whether the behavioural response to any given condition is a manifestation of EA.