Development and validation of the Diabetes Numeracy Test (DNT)

Mary Margaret Huizinga¹^,2^,3 , Tom A Elasy¹^,2^,3 , Kenneth A Wallston⁴ , Kerri Cavanaugh⁵ , Dianne Davis³ , Rebecca P Gregory³ , Lynn S Fuchs⁶ , Robert Malone⁷ , Andrea Cherrington⁸ , Darren A DeWalt⁷ , John Buse⁷ , Michael Pignone⁷ and Russell L Rothman¹^,2^,3

¹Division of General Internal Medicine and Public Health, Department of Medicine, Center for Health Services Research, Vanderbilt University Medical Center, Nashville, USA

²VA Quality Scholars Program, VA Tennessee Valley Healthcare System, Nashville, USA

³Diabetes Research and Training Center, Vanderbilt University Medical Center, Nashville, USA

⁴School of Nursing, Vanderbilt University Medical Center, Nashville, USA

⁵Division of Nephrology, Department of Medicine, Vanderbilt University Medical Center, Nashville, USA

⁶Peabody College of Education, Vanderbilt University, Nashville, USA

⁷Department of Medicine, University of North Carolina, Chapel Hill, USA

⁸Department of Medicine, University of Alabama, Birmingham, USA

author email corresponding author email

BMC Health Services Research 2008, 8:96doi:10.1186/1472-6963-8-96


Published:	1 May 2008

Abstract

Background

Low literacy and numeracy skills are common. Adequate numeracy skills are crucial in the management of diabetes. Diabetes patients use numeracy skills to interpret glucose meters, administer medications, follow dietary guidelines and other tasks. Existing literacy scales may not be adequate to assess numeracy skills. This paper describes the development and psychometric properties of the Diabetes Numeracy Test (DNT), the first scale to specifically measure numeracy skills used in diabetes.

Methods

The items of the DNT were developed by an expert panel and refined using cognitive response interviews with potential respondents. The final version of the DNT (43 items) and other relevant measures were administered to a convenience sample of 398 patients with diabetes. Internal reliability was determined by the Kuder-Richardson coefficient (KR-20). An a priori hypothetical model was developed to determine construct validity. A shortened 15-item version, the DNT15, was created through split sample analysis.

Results

The DNT had excellent internal reliability (KR-20 = 0.95). The DNT was significantly correlated (p < 0.05) with education, income, literacy and math skills, and diabetes knowledge, supporting excellent construct validity. The mean score on the DNT was 61% and took an average of 33 minutes to complete. The DNT15 also had good internal reliability (KR-20 = 0.90 and 0.89). In split sample analysis, correlations of the DNT-15 with the full DNT in both sub-samples was high (rho = 0.96 and 0.97, respectively).

Conclusion

The DNT is a reliable and valid measure of diabetes related numeracy skills. An equally adequate but more time-efficient version of the DNT, the DNT15, can be used for research and clinical purposes to evaluate diabetes related numeracy.