The Hot Flash Related Daily Interference Scale: cutoffs, minimally important differences, and a revised short version
One of the first psychometrically developed measures available for clinicians and researchers to assess VMS bother was the Hot Flash Related Daily Interference Scale (HFRDIS).8 Comprised of 10 items, the scale measures the women's self-perceived interference on 10 aspects of their lives in the past week. An average score on the items is calculated, ranging from 0 to 10, with higher scores indicating a greater degree of interference. The measure is a popular and well-used measure throughout the world, and available in 12 languages at the time of this publication.
However, in their article, Carpenter et al9 noted several areas for improvement. These included the dearth of evaluated cutoffs, and minimally important differences (MIDs) in scores (the minimum changes in scores perceived as important by patients10) from which to help inform clinician response to patients’ experience of menopause symptoms. In addition, anecdotal observations by the authors suggest possible redundant items in the HFRDIS as several items are often left empty or given a zero by women, suggesting a shorter measure could be produced. Their study therefore attempted to address these issues and achieve three key aims: (1) to reduce the length of the HFRDIS; (2) develop useful cutoffs for both the original HFRDIS and shortened version; and (3) to identify MIDs for both measures.
Using a sample of 899 peri- and post-menopausal women participants in three Menopause Strategies: Finding Lasting Answers for Symptoms and Health trials in the United States,11-15 Carpenter et al9 produced a psychometrically valid condensed three-item measure called the Hot Flash Interference scale (HFI), which focuses on hot flash interference with sleep, mood, and concentration. The study also suggests three cutoff points for mild (score 0-3.9), moderate (score 4-6.9), and severe (score 7-10) VMS interference with life on either the original HFRDIS or the HFI scales. Finally, MIDs of 1.66 and 2.34 for the HFRDIS and HFI, respectively, were found to identify clinically appropriate changes to patient perceived symptom interference.
The study makes a clear and valuable contribution to both practice and research. The use of multiple measures and assessments are typical in clinical environments and research. These are not only difficult to administer, but place additional burden on respondents, and may result in incomplete data being returned. Partly for these reasons, scale brevity is an important characteristic of any measurement tool and the removal of superfluous items is encouraged.16 The condensed three-item HFI scale to measure hot flash interference is therefore a highly useful resource that will allow quicker completion and calculation of VMS bother. The cutoffs and MIDs, now evaluated, also allow for easier comparisons across patients and samples and promoting greater consistency in interpretation.
One key strength of the research was the consideration and adoption of both a logical and empirical approach to refining the measure and ensuring validity. This included the use of both experts and appropriate statistical analyses, respectively. Content validity and construct (convergent) validity, for example, were assessed and demonstrated convincing evidence for the condensed scale. Internal reliabilities were also sufficiently confirmed using Cronbach alphas. Another notable strength was the theoretically driven approach to evaluating cutoff points.