B-4 THE NUMERACY UNDERSTANDING IN MEDICINE INSTRUMENT (NUMI): A NEW MEASURE OF HEALTH NUMERACY DEVELOPED USING ITEM RESPONSE THEORY

Monday, October 25, 2010: 2:15 PM
Grand Ballroom Centre (Sheraton Centre Toronto Hotel)
Marilyn Schapira, MD, MPH1, Cindy M. Walker, Ph.D.2, Kathlyn Fletcher, MD, MPH3, Pamela Ganschow, MD4, Elizabeth Jacobs, MD, MPP5, Sam Del Pozo, B.S.4 and Carrie Schauer, BS1, (1)Medical College of Wisconsin, Milwaukee, WI, (2)University of Wisconsin, Milwaukee, WI, (3)Medical, Milwaukee, WI, (4)Rush University Medical Center, Chicago, IL, (5)John Stroger Hospital & Rush Medical College, Chicago, IL

Purpose: To develop a test of a measure of health numeracy  that is based on an empirically derived framework, cross-culturally equivalent for Hispanic and Non-Hispanic populations, and uses  Item Response Theory scaling methods.

Method: A cross-cultural approach was used in the development of the Numeracy Understanding in Medicine Instrument (NUMi).    Qualitative methods used to generate the item bank (n=110) included focus groups, convening of an expert panel, and cognitive interviews.   Participants (n=1000) were recruited from community and clinical populations to test the items.    A 2-Parameter IRT model was used for analysis of the first 500 respondents.   Participants also responded to the Test of Functional Health Literacy in Adults-Short Form (S-TOFHLA) and a cognitive reasoning and aptitude test (Wonderlic).   A sample (n=200) of participants were also administered the Lipkus numeracy scale and a mathematic achievement test (WRAT-M).

Result: Of the first 500 participants 50% were White and 40% were Black.  Over 30% were Hispanic and 40% had a high school level education.  Based upon the IRT parameters of difficulty (range of -3.0 t0 3.0) and discrimination (range of 0 to 3.0), 20 items were chosen to form the NUMi.  The most difficult items in each domain assessed the following skills:  1) Determining how many 500 mg pills add up to 3 grams (number sense), 2) interpreting a risk of 2/1000 in a pictograph (tables and graphs), 3) interpreting a relative risk reduction (probability), and 4) interpreting the meaning of a p-value that is < 0.05 (statistics).  The Test Information Function peaked at a difficulty level of -1.0 indicted that the test is most discriminating for people  with lower than average health numeracy.  Test performance was positively associated with cognitive reasoning (0.79) and print health literacy (0.54).

Conclusion: The NUMi is a 20 item paper and pencil test that measures an empirically based construct of health numeracy.  In future work, a computerized adaptive test will be developed in which items are selected based upon the ability of the respondent leading to a shorter test that will reduce respondent burden and allow for oral or print administration.  The NUMi will provide a feasible and valid assessment of health numeracy skills for use in both research and clinical settings.