Background: Self-reported data are a common source of information about drug exposure. Modes of data collection differ considerably and the questionnaire's structure may affect prevalence estimates. We compared the recall of medication use evaluated by means of two questionnaires differing in structure and length.
Methods: Drug utilization was assessed by two alternative versions of a questionnaire (A - 4 pages, including specific questions for 12 indications/pharmacological groups and one question for "other medicines"; B - 1 page, including 1 open-ended question to cover overall drug consumption). Each of 32 classes in a private University in Maputo, Mozambique, was randomly assigned questionnaire A (233 participants) or B (276 participants). Logistic regression (allowing for clustering by classroom) was used to compare the two groups in terms of socio-demographic characteristics and medication used during the previous month.
Results: Overall, 67.4% of the subjects had used at least one drug during the previous month. The following prevalences were greater among participants completing questionnaire A: use of drugs from two or more pharmacological groups (60.5% vs. 34.4%, p < 0.001), use of two or more drugs (66.2% vs. 43.0%, p < 0.001), and use of antibiotics (14.6% vs. 6.9%, p = 0.001), antifungals (9.4% vs. 4.0%, p = 0.013), antiparasitics (5.6% vs. 1.8%, p = 0.031) and antacids (8.6% vs. 3.6%, p = 0.024). Information about duration of treatment and medical advice was more complete with version A.
Conclusion: The indication/drug-specific questions (questionnaire A) revealed a significantly higher prevalence of use of medicines - antibiotics, antifungals, antiparasitics and antacids - without compromising the completeness of the information.