People's intentions are mainly determined by perceived barriers and obstacles regarding blood donations. This suggests that promotional strategies should focus on the elimination of barriers to action as well as the development of a higher perception of control. Also, messages should be adapted to the targeted population, based on their previous blood donation behaviour (i.e. never donors vs. ever donors).

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The theory of planned behavior presents clear operational definitions of attitudes, subjective norm, perceived behavioral control, and each of their corresponding belief‐based measures. Theoretically, the direct and indirect measures of a given construct must be closely correlated. Empirical results, however, indicate that this is not always the case. In the present study, 2 of the factors that could be responsible for this situation‐namely, the scaling of the variables defining each belief‐based construct and the adequacy of using an expectancy‐value model within the belief‐based measures‐were verified among a data set of 16 studies concerned with the application of the theory of planned behavior to the field of health. The results indicate that the scaling method used affected the correlation coefficients between indirect and direct measures. However, the face validity of these scaling methods must be demonstrated. The results also support the idea that, in most cases, using the expectancy‐value model is no better than using only one arm of the belief‐based measure.

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The aim of this study was to verify the validity of a new self-reported questionnaire designed to assess nonadherence to antiretroviral medication among patients with HIV. Two hundred fifty-six patients from four clinics participated in a prospective longitudinal study. The questionnaire was designed to measure if patients with HIV were taking less than the total number of antiretroviral pills prescribed by their physician. Change in viral load was used as the criterion for validity analyses. Self-reported adherence, viral load and CD4 cell count were assessed at T0 (baseline), T3 (3-month), and T6 (6-month). The findings indicated that the questionnaire had adequate validity (sensitivity, 71%; specificity, 72%; correct classification, 72%; odd ratio, 6.15). These best values were obtained when the analyses excluded individuals with an unstable viral load and a CD4 cell count of less than 200 copies per milliliter over the 6-month follow-up period. This study has shown that this questionnaire has satisfactory psychometric qualities to assess nonadherence to antiretroviral medication among patients with HIV. The questionnaire is brief, simple, and can be used in both clinical or research settings regardless of the patients' antiretroviral regimens.