Performance of two questionnaires to measure treatment adherence in patients with Type-2 diabetes.
BACKGROUND
Most valid methods to measure treatment adherence require time and resources, and they are not easily applied in highly demanding Primary Health Care Clinics (PHCC). The objective of this study was to determine sensitivity, specificity, predictive values, likelihood ratios, and post-test probabilities of two novel questionnaires as proxy measurements of treatment adherence in Type-2 diabetic patients.


METHODS
Two questionnaires were developed by a group of experts to identify the patient's medical prescription knowledge (knowledge) and their attitudes toward treatment adherence (attitudes) as proxy measurements of adherence. The questionnaires were completed by patients receiving care in PHCC pertaining to the Mexican Institute of Social Security in Aguascalientes (Mexico). Pill count was used as gold standard. Participants were selected randomly, and their oral hypoglycemic prescriptions were studied. The main outcome measures for each questionnaire were sensitivity, specificity, predictive values, likelihood ratios, and post-test probabilities, all as an independent questionnaire test and in a serial analysis.


RESULTS
Adherence prevalence was 27.0% using pill count. Knowledge questionnaire showed the highest sensitivity (68.1%) and negative predictive value (82.2%), the lowest negative likelihood ratio (0.58) and post-test probability for a negative result (0.16). Serial analysis showed the highest specificity (77.4%) and positive predictive value (40.1%) as well as the highest positive likelihood ratio (1.8) and post-test probability for a positive result (0.39).


CONCLUSIONS
Medical Prescription Knowledge questionnaire showed the best performance as proxy measurement to identify non-adherence in type 2 diabetic patients regarding negative predictive value, negative likelihood ratio, and post-test probability for a negative result. However, Medical Prescription Knowledge questionnaire performance may change in contexts with higher adherence prevalence. Therefore, more research is needed before using this method in other contexts.
Prado-Aguilar
Carlos A
CA
Unidad de Investigación Epidemiológica y en Servicios de Salud, Hospital General de Zona N degrees 1, Instituto Mexicano del Seguro Social, Aguascalientes, Ags., México. carlospa@uiessags.com
Martínez
Yolanda V
YV
Segovia-Bernal
Yolanda
Y
Reyes-Martínez
Rosendo
R
Arias-Ulloa
Raul
R
D000367:Age Factors; D000368:Aged; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000175:diagnosis / Q000628:therapy*; D003927:Diet, Diabetic; D005260:Female; D005500:Follow-Up Studies; D007722:Health Knowledge, Attitudes, Practice; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage; D008019:Life Style; D016013:Likelihood Functions; D008297:Male; D008800:Mexico; D008875:Middle Aged; D010349:Patient Compliance / Q000706:statistics & numerical data*; D011237:Predictive Value of Tests; D011788:Quality of Life; D012307:Risk Factors; D012680:Sensitivity and Specificity; D012737:Sex Factors; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires; D016896:Treatment Outcome
D007004:Hypoglycemic Agents