Development and validation of the Diabetes Numeracy Test (DNT).
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).


CONCLUSIONS
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.
Huizinga
Mary Margaret
MM
Division of General Internal Medicine and Public Health, Department of Medicine, Center for Health Services Research, Vanderbilt University Medical Center, Nashville, USA. mary.margaret.huizinga@vanderbilt.edu
Elasy
Tom A
TA
Wallston
Kenneth A
KA
Cavanaugh
Kerri
K
Davis
Dianne
D
Gregory
Rebecca P
RP
Fuchs
Lynn S
LS
Malone
Robert
R
Cherrington
Andrea
A
Dewalt
Darren A
DA
Buse
John
J
Pignone
Michael
M
Rothman
Russell L
RL
D003920:Diabetes Mellitus; D004521:Educational Measurement; D004522:Educational Status; D005260:Female; D006801:Humans; D008297:Male; D008433:Mathematics; D015203:Reproducibility of Results; D014481:United States