Beliefs about Medicines Questionnaire Specific
The BMQ-S consists of 10 items, with 5 items for beliefs about necessity (e.g. “My health in de future will depend on these medicines”) and 5 items about concerns (e.g. “Having to take these medicines worries me”). All items are rated on a 5-point Likert Scale from 1 (strongly disagree) to 5 (strongly agree), hence a sum scale score of 5 to 25 for necessity and concern beliefs subscales. The difference between necessity and concern sum scale scores (NC-differential) is between -20 and +20, with a total positive score meaning that advantages of DOAC use outweigh disadvantages. On the basis of the necessity and concern scores, patients are also categorized as accepting (necessity >16, concern ≤13), ambivalent (necessity >16, concern >13), sceptical (necessity ≤16, concern >13) or indifferent (necessity ≤16, concern ≤13) [21]. The BMQ consists of one more item that is not used in the shorter BMQ-S for calculating necessity and concern beliefs scores. Because this item (question 11) is about a concern believe about side effects of DOACs (“These medicines have unpleasant side effects”) we have included it as well to compare with results obtained from the side effect burden questionnaire [17].