Research by Ziegler, Lew and Singer62 suggests that doctors may not be very critical of verbal promotional information. They found 12 inaccurate statements (i.e. statements which contradicted the Physicians’ Desk Reference or literature quoted by or handed out by the sales representative) in brief presentations given by sales representatives at industry-sponsored lunches. When they later surveyed 27 doctors who attended these presentations only seven recalled hearing the representative make a claim that they knew to be false.
Similarly, Sansgiry et al.68 in the USA found that consumers may not be very critical of advertisements. They compared consumers' (students in non-health related subjects) assessments of 14 advertisements for over-the-counter medicines with those of experts (clinical pharmacists). Each advertisement was viewed by nine participants. The consumers rated the advertisements as more factual, good and complete than the experts, even though information on contraindications and side-effects was missing. Consumers were not able to identify misleading and inaccurate information. Only 20% of consumers identified side-effects correctly and 14% contraindications.
A 1982 study by Avorn, Chen and Hartley is very commonly quoted as evidence of the negative impact of promotion63. They surveyed doctors about two drugs about which there was significant disagreement between scientific and commercial sources of information. There was no scientific evidence of benefit from cerebral vasodilators and evidence of minimal efficacy for propoxyphene. However promotional material presented them as efficacious and reliable. Avorn et al. argued that by looking at which of these beliefs doctors held they could see which type of information source doctors were really influenced by. Most of the 85 Boston doctors they surveyed said that they relied mainly on academic sources of information, and that advertising, sales representatives and patient preference were minimal influences on their prescribing. However their beliefs about cerebral vasodilators and propoxyphene tended to be more consistent with the commercial literature than with the scientific consensus. Nearly half (48%) of the doctors who supported the use of vasodilators stated that they were more influenced by scientific rather than commercial sources of information. Avorn et al. say that this discrepancy between where the doctors’ beliefs seemed to come from, and their statements about what influenced them could be because doctors are unaware of how commercial sources influence them, or it could be because doctors are unwilling to admit this influence.
The Avorn et al. study is particularly important because it is very widely quoted. Therefore it is important to analyse it critically, and to suggest how further research might explore its findings. The study was simple, presumably inexpensive, yet cleverly designed. However it could be criticised in several ways. Avorn et al. focus on two sources of influence: ‘scientific’ and ‘commercial’. However more doctors in the study rated their own ‘training and clinical experience’ as a very important influence on their prescribing than rated either scientific or commercial sources in this way. At the time of the study there was a clear disagreement between the scientific and commercial views of the medicines studied, but the authors suggest incidentally that this had not previously been the case (e.g. the link between cerebral blood flow and senile dementia is “a concept now abandoned”). Doctors holding the ‘commercial’ belief could be holding on to a view taught in medical school or learnt from other doctors in the past and/or reinforced by the placebo effect in practice (their ‘clinical experience’). Avorn et al. do not convincingly demonstrate that the doctors’ ideas came from commercial sources. They may instead have resulted from their training and beliefs that ‘clinical experience’ is more valuable than scientific evidence-based medicine. It may be hard for doctors to exclude medicines from their prescribing repertoires if they learnt about them in medical school and they seem to work in practice.
Greenwood’s study64 included a sub-study that repeated Avorn et al.’s method. He surveyed 332 GPs, in one area of England, about the use of four medicines on which scientific and commercial views conflict. The commercial view was held by 77% of doctors for one drug, and by 55%, 28% and 13% for the others. This study was a PhD thesis, and is difficult to obtain. Summaries are published in HAI News, No 48, August 198990 and in Lexchin91.
Similarly, in Peru, Cardenas and Isenrich92 found that while doctors said that they relied mostly on medical literature for their drug information, in fact their self-reported prescribing decisions were clearly not based on this.
Ferry et al.69 found that doctors who reported relying on advertising as a source of information achieved lower scores on a test of knowledge about prescribing for the elderly. Only 25% of the doctors who received this mailed survey responded to it.
CONCLUSION: Doctors’ attitudes are influenced by promotion much more than they think.