Association of Numeracy and Diabetes Control

20 May 2008 | Volume 148 Issue 10 | Pages 737-746

Background: The influence of a patient's quantitative skills (numeracy) on the management of diabetes is only partially understood.

Objective: To examine the association between diabetes-related numeracy and glycemic control and other diabetes measurements.

Design: Cross-sectional survey.

Setting: 2 primary care and 2 diabetes clinics at 3 medical centers.

Participants: 398 adult patients with type 1 or type 2 diabetes mellitus enrolled between March 2004 and November 2005.

Measurements: Health literacy, general numeracy, and diabetes-related numeracy assessed by using the Rapid Estimate of Adult Literacy in Medicine; the Wide Range Achievement Test, 3rd edition; and the Diabetes Numeracy Test (DNT), respectively. The primary outcome was most recent level of hemoglobin A_1c. Additional measurements were diabetes knowledge, perceived self-efficacy of diabetes self-management, and self-management behaviors.

Results: The median DNT score was 65% (interquartile range, 42% to 81%). Common errors included misinterpreting glucose meter readings and miscalculating carbohydrate intake and medication dosages. Lower DNT scores were associated with older age, nonwhite race, fewer years of education, lower reported income, lower literacy and general numeracy skills, lower perceived self-efficacy, and selected self-management behaviors. Patients scoring in the lowest DNT quartile (score <42%) had a median hemoglobin A_1c level of 7.6% (interquartile range, 6.5% to 9.0%) compared with 7.1% (interquartile range, 6.3% to 8.1%) in those scoring in the highest quartile (P = 0.119 for trend). A regression analysis adjusted for age, sex, race, income, and other factors found a modest association between DNT score and hemoglobin A_1c level.

Limitation: Causality cannot be determined in this cross-sectional study, especially with its risk for unmeasured confounding variables.

Conclusion: Poor numeracy skills were common in patients with diabetes. Low diabetes-related numeracy skills were associated with worse perceived self-efficacy, fewer self-management behaviors, and possibly poorer glycemic control.

Editors' Notes Context Self-management of diabetes often involves interpretation of quantitative information and performing calculations. Poor numeracy skills could have an effect on diabetes management. Contribution The authors measured diabetes management–related numeracy skills and hemoglobin A1c in a sample of 398 diabetic patients from primary care clinics and diabetes clinics at 3 medical centers. Many could not calculate the calories in a bag of potato chips or recognize a very low blood glucose value. Hemoglobin A1c levels were slightly worse in patients with poor diabetes-related numeracy, more so if young, less literate, or with recent diagnosis. Implication Poor diabetes-related numeracy is common but is weakly related to glycemic control. —The Editors

 

Author and Article Information

From Vanderbilt University School of Medicine and Veterans Affairs Tennessee Valley Healthcare System, Nashville, Tennessee; University of North Carolina, Chapel Hill, North Carolina; and University of Alabama, Birmingham, Alabama.

Grant Support: From the American Diabetes Association (Novo Nordisk Clinical Research Award), the Pfizer Clear Health Communication Initiative, and the Vanderbilt Diabetes Research and Training Center (National Institute of Diabetes and Digestive and Kidney Diseases [NIDDK] 5P60DK020593). Dr. Rothman is also currently supported by an NIDDK Career Development Award (NIDDK 5K23DK065294).

Potential Financial Conflicts of Interest: Honoraria: D.A. DeWalt (Pfizer), R.L. Rothman (Pfizer). Grants received: D.A. DeWalt (Pfizer), R.L. Rothman (Pfizer).

Reproducible Research Statement: Study protocol, statistical code, and data set: Available, with institutional approval, from Dr. Rothman (e-mail, russell.rothman{at}vanderbilt.edu).

Requests for Single Reprints: Russell L. Rothman, MD, MPP, Vanderbilt University Medical Center, 6100 Medical Center East, North Tower, Vanderbilt Center for Health Services Research, Nashville, TN 37232-8300; e-mail, russell.rothman{at}vanderbilt.edu.

Current Author Addresses: Dr. Cavanaugh: Vanderbilt University, 1161 21st Avenue South, 5-3223 Medical Center North, Nashville, TN 37232.

Drs. Huizinga and Rothman: Vanderbilt University, 1215 21st Avenue South, 6100 Medical Center East, North Tower, Nashville, TN 37232.

Dr. Wallston: Vanderbilt University, 421 Godchaux Hall, 461 21st Avenue South, Nashville, TN 37240.

Drs. Gebretsadik and Shintani: Vanderbilt University, 1211 21st Avenue South, S-2323 Medical Center North, Nashville, TN 37232.

Dr. Davis: Vanderbilt University, 1211 21st Avenue South, 3061 Medical Arts Building, Nashville, TN 37212.

Dr. Pratt Gregory: Vanderbilt University Diabetes Center, 315 Med Arts, 1211 21st Avenue South, Nashville, TN 37212.

Dr. Fuchs: Vanderbilt University, 228 Peabody, 230 Appleton Place, Nashville, TN 37220.

Drs. Malone, Pignone, and DeWalt: University of North Carolina Chapel Hill, 5039 Old Clinic Building CB #7110, Chapel Hill, NC 27599.

Dr. Cherrington: University of Alabama, 1530 3rd Avenue South, Birmingham, AL 35294.

Dr. Elasy: Vanderbilt University, 1215 21st Avenue South, 8210 Medical Center East, South Tower, Nashville, TN 37232.

Author Contributions: Conception and design: R.L. Rothman, K.A. Wallston, R. Pratt Gregory, L. Fuchs, D.A. DeWalt, T.A. Elasy.

Analysis and interpretation of the data: R.L. Rothman, K. Cavanaugh, M.M. Huizinga, T. Gebretsadik, A. Shintani, M. Pignone, D.A. DeWalt.

Drafting of the article: R.L. Rothman, K. Cavanaugh, A. Cherrington.

Critical revision of the article for important intellectual content: R.L. Rothman, K. Cavanaugh, M.M. Huizinga, K.A. Wallston, T. Gebretsadik, R. Malone, A. Cherrington, M. Pignone, D.A. DeWalt, T.A. Elasy.

Final approval of the article: R.L. Rothman, K. Cavanaugh, M.M. Huizinga, K.A. Wallston, L. Fuchs, R. Malone, A. Cherrington, M. Pignone, D.A. DeWalt, T.A. Elasy.

Provision of study materials or patients: R.L. Rothman, K.A. Wallston, D. Davis, R. Malone, M. Pignone.

Statistical expertise: T. Gebretsadik, A. Shintani.

Obtaining of funding: R.L. Rothman.

Administrative, technical, or logistic support: R.L. Rothman, R. Malone, T.A. Elasy.

Collection and assembly of data: R.L. Rothman.

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