How Many Exposures Are Enough?

In 1966 Colin McDonald, then working for the British Market Research Bureau in London, carried out a research project for J. Walter Thompson . This was a study of the relationship between advertising exposure and buying behavior in a number of packaged goods markets, using a single source diary panel. (A 'single source' panel, in this sense, collects detailed information for each individual both on what brands were bought, and what ads were seen, each day.) This study was not intended, at the time, to address the questions of ‘effective frequency’, but the more fundamental issue of whether short term advertising effects on purchasing behavior could be proven to exist. The most famous finding of this study (as reported at the time) was that one exposure to advertising between two purchase occasions had no positive effect on brand choice; that two exposures did have an effect, that three had a little more; and that above three exposures there were no increased effects.

The McDonald Study, after its brief moment of glory, was unjustly neglected by many advertising agency people; they were not very interested in effects which appeared to be very short term and rather small, and they preferred talking to their clients about the long term effects of advertising on brand image. But the study was leapt on enthusiastically by media planners who had been asking questions about effective frequency. Nothing like the McDonald study had ever been done before. Now the data appeared to show that a ‘threshold’ of two exposures did exist, and also that the effect of advertising peaked at three exposures. The implication for media planners was that they should maximize the number of people receiving two exposures in a purchase interval, and minimize the number receiving more than three. (This is actually very difficult to put into practice, but in theory, at least, it became an established principle.)

This ‘three exposure’ principle received apparent confirmation when it was matched to a psychological theory developed independently by Dr Herbert Krugman, then head of market research at General Electric in the USA. Krugman argued that consumer response to an ad went through three stages. The first time it was seen, the respondent would just ask ‘what is it?’. On the ‘second exposure’ the viewer was able to evaluate the communication - ‘what of it?’. Having made sense of the message, the ‘third exposure’ would merely be a repetition and after this the subject would begin to ‘disengage’. Krugman developed this argument in various papers published during the 1970's.

In 1979 the Association of National Advertisers in New York produced a book authored by Mike Naples, called Effective Frequency. This reviewed the complex issues involved, and all the relevant experimental findings, starting from Ebbinghaus' research into memory decay in the 1890's. In pride of place was the McDonald Study, and McDonald's own paper about it from the 1970 ESOMAR Congress was included in full as an appendix. The book drew a number of conclusions, and was widely understood to endorse the ‘three exposure theory’ (Dr Krugman contributed the foreword to the volume). The first conclusion of Effective Frequency began, in fact, with the words: ‘One exposure of an advertisement to a target group consumer within a purchase cycle has little or no effect in all but a minority of circumstances...’

When Colin McDonald accepted a brief from the ANA in 1993 to update Effective Frequency he was already becoming uneasy with this conclusion, which was also being challenged by more recent research. In particular he was aware of work being done by Professor John Philip Jones in the USA (published in 1995 as a book, When Ads Work). Using data from the Nielsen single source panel and a similar conceptual approach to the McDonald Study (though not identical), Jones claimed decisive evidence for an advertising effect on behavior after one exposure, with strongly diminishing returns above two.

The result is a substantial rewrite of the earlier book, with some significantly different conclusions. The new book follows much of the original structure, and like the original it reviews a wide body of published evidence. But at the core of the book is a detailed re-examination by McDonald of his 1966 study, which makes it very clear that the ‘two exposure threshold’ was, in fact, an illusion - an artifact of one particular type of analysis which was thereafter extensively quoted out of context. The findings of Jones and McDonald are therefore consistent with each other, and with other single source studies which are referred to in the book.

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