Psychometric properties of the Revised Fibromyalgia Impact Questionnaire (FIQR) - a contribution to the Portuguese validation of the scale

Background: Fibromyalgia (FM) remains a relatively misunderstood and clinically challenging condition that impact significantly in the individual's life, impairing global functioning and diminishing quality of life. Management is complex and frequently unsatisfactory, requiring personal tailoring and adaptation of interventions according to the fluctuations of the disease manifestations and their response to therapy. The use of comprehensive and quantified assessment tools constitutes, therefore, an essential component of the management of patients with FM. The Revised Fibromyalgia Impact Questionnaire (FIQR) is currently one of the most used and well validated instruments to assess functional (in) capacity and global impact of FM and associated symptoms. Objectives: To translate to Portuguese the FIQR and to study its psychometric properties. Material and Methods: The total sample comprised 103 women with fibromyalgia, defined according to the established criteria for FM. A self-report battery composed by the Revised Fibromyalgia Impact Questionnaire (FIQR), and the Portuguese versions of Beck Depression Inventory-II (BDI-II) and the Profile of Mood States (PoMS) was administered. The FIQR was re-administered to twenty-four participants, six weeks after the first evaluation. Internal reliability was assessed through Cronbach's alpha, corrected item-total score correlations and alpha if item deleted. Spearman and Pearson correlations along with repeated measures tests were computed to assess the temporal stability of the scale. Convergent and divergent validity were assessed via Spearman and Pearson correlations. Results: The FIQR demonstrated a good to very good internal consistency (from alpha=0.87 to alpha=0.94). All items correlated to a good degree (above 0.30) to the total score and contributed significantly to the overall reliability. Moreover, FIQR presented a good temporal stability (from r=.617 to r=.886, p=.001) and favorable convergent and discriminant validity with depressive symptoms (r >.289, p=.01) and positive (r > -. 186, p >.05) and negative affect (r >.206, p=.05). Conclusions: The Portuguese version of the FIQR demonstrated good psychometric properties, which renders it a proper and valuable tool to be used in different settings.