Many descriptive studies clearly show that much promotional material contains inaccuracies, or at least presents very selective accounts of the evidence about the drug presented^62,63,64. The question this review addresses is whether and how far promotion (including these inaccuracies and biases) affects the attitudes and knowledge of those who are exposed to it.

Very little research has looked specifically at the effect of promotion on attitudes, much more has examined the effect of promotion on knowledge. The studies here are part of a field of research into the determinants of prescribing - how doctors learn about drugs, and how they come to prescribe new products.

Most of the studies discussed in this review are really about how much doctors report using promotion as a source of information (either for all drugs, or particularly for new drugs) rather than about effects of promotion on attitudes or knowledge. They are included because they provide information relevant to the question of whether promotion affects prescribers’ knowledge.

Some studies look directly at the impact of promotion on attitudes and knowledge, by using an experimental approach⁶⁵, by interviewing people about previous exposure⁶⁶, or by following up participants in a promotional event⁶⁷. Others approach the question in a more sophisticated or indirect way. Ziegler et al.⁶² look at whether doctors notice and remember errors in promotion. Sansgiry et al.⁶⁸ look at whether consumers are aware of information missing from advertisements. Others^63,64 look at doctors’ attitudes or knowledge in areas where there is disagreement between commercial and scientific information and infer the impact of promotion from this. Ferry et al.⁶⁹ directly assessed knowledge of prescribing for the elderly and looked at it in relation to self-assessed reliance on promotion.

The methods that have been used in this area are not capable of producing certainty about causal relationships. Firstly both exposure to promotion, and knowledge and attitudes about drugs, are often assessed using self-report data. Secondly the relationship between them is often also assessed using self-report. That is, doctors are asked how much their prescribing is influenced by promotion. Self-report can be misleading when doctors’ beliefs are inaccurate (e.g., they may believe that they are exposed less often than they are), or when their answers to questions are biased towards being more socially acceptable than what they really believe.