How Often Should You Advertise?

I belong to an online community interested in social marketing.  

This very active group of people generously shares research and experiences on strategies that encourage people to change personal and group behaviour to achieve positive personal, community, environmental or other outcomes.

Recently a forum member asked "...is there a certain number of times that a consumer needs to be exposed to a message before it leads to a behavior change?"

I do a lot of advertising so the topic captured my attention.  

I was particularly impressed with Linda Brennan's response. Linda is Professor of Advertising at the Royal Melbourne Institute of Technology (RMIT).  She replied (quoted in full):

"The rule of thumb in advertising is 3 repeats in order for people to remember it. There are some generalisations about this idea that suggest that recall is a good first step in generating attention.

However, behaviour change is not about exposure to the message; it is about engagement with the message. That is, it must be relevant to the audience, accepted and credible, they must have formed some sort of attachment to the ideas embedded in the message/exposure and then they must have actively decided to behave differently. Some time after that comes behaviour and only then if the social ecology (environment) in which they live allows for them to behave differently to previous behaviours.

So, do not over expose your message and hope it will work for you (it won't)."

Someone else highlighted research by Gerard J Tellis of the University of Southern California and his research paper titled Effective Frequency: One Exposure or Three Factors? 

Advertising can be a powerful weapon to introduce an issue or to reinforce a message, but in this age of communications-saturation it has long since lost favour as a silver bullet.