Psychometric properties of the hypoglycemia fear survey-ii for adults with type 1 diabetes

OBJECTIVE

To perform the first comprehensive psychometric evaluation of the Hypoglycemia Fear Survey-II (HFS-II), a measure of the behavioral and affective dimensions of fear of hypoglycemia, using modern test-theory methods, including item-response theory (IRT).

RESEARCH DESIGN AND METHODS

Surveys completed in four previous studies by 777 adults with type 1 diabetes were aggregated for analysis, with 289 subjects completing both subscales of the HFS-II and 488 subjects completing only the Worry subscale. The aggregated sample (53.3% female, 44.4% using insulin pumps) had a mean age of 41.9 years, diabetes duration of 23.8 years, HbA_1c value of 7.7%, and 1.4 severe hypoglycemic episodes in the past year. Data analysis included exploratory factor analysis using polychoric correlations and IRT. Factors were analyzed for fit, trait-level locations, point-measure correlations, and separation values.

RESULTS

Internal and test-retest reliability was good, as well as convergent validity, as demonstrated by significant correlations with other measures of psychological distress. Scores were significantly higher in subjects who had experienced severe hypoglycemia in the past year. Factor analyses validated the two subscales of the HFS-II. Item analyses showed that 12 of 15 items on the Behavior subscale, and all of the items on the Worry subscale had good-fit statistics.

CONCLUSIONS

The HFS-II is a reliable and valid measure of the fear of hypoglycemia in adults with type 1 diabetes, and factor analyses and IRT support the two separate subscales of the survey.The Hypoglycemia Fear Survey (HFS), first published in 1987 (1), originally was developed to measure behaviors and worries related to fear of hypoglycemia (FOH) in adults with type 1 diabetes. Both the original HFS (HFS-I) and the revised version (HFS-II) are composed of two subscales, the Behavior (HFS-B) and Worry (HFS-W). HFS-B items describe behaviors in which patients may engage to avoid hypoglycemic episodes and/or their negative consequences (e.g., keeping blood glucose BG] levels above 150 mg/dL, making sure other people are around, and limiting exercise or physical activity). HFS-W items describe specific concerns that patients may have about their hypoglycemic episodes (e.g., being alone, episodes occurring during sleep, or having an accident). Since it was first published, the HFS, in its original form and subsequent revisions, has been used in >60 published studies and numerous clinical trials and has been translated into over 50 languages. The survey also is commonly used in studies of people with type 2 diabetes to better understand their experiences of hypoglycemia (2). In addition, the authors have developed alternative versions of the HFS for use with pediatric patients with type 1 diabetes and their parents, as well as spouses and significant others of adults with diabetes (3–5).Despite its widespread use, the only comprehensive study to address the psychometric properties of the U.S. HFS was published >15 years ago and focused on the HFS-I, which is no longer in use (6). Since then, based on subsequent studies, the scale has been significantly revised, leaving only 18 of 33 items unchanged from the original version from 1987. Although there is some evidence for the reliability and validity of the HFS-II (2,7), no comprehensive study of its psychometric properties has been conducted with a large sample. In addition, psychometric results of previous studies included only classical test-theory methods that have not acknowledged the categorical nature of HFS data. Modern test procedures, such as item-response theory (IRT), are better suited to analyze categorical data and can provide valuable information about item quality, including response option use, fit, and endorsement difficulty (8).For researchers and clinicians interested in using the HFS-II, this lack of supporting psychometric data presents many obstacles not the least of which is the inability to interpret scores in a clinically meaningful way. The purpose of the current study was to conduct a comprehensive psychometric investigation of the HFS-II U.S. English adult version using a large aggregate sample of data collected at our laboratory over the past decade and using modern test-theory methods. The following were the hypotheses tested: 1) that the HFS-II is a reliable and valid measure of FOH and 2) that factor analysis will yield a two-factor structure reflecting the two subscales of the survey.