The agency has carried out what it claims is the UK's largest study into the influence of word of mouth on selling brands.
The survey of 10,000 consumers reveals that 76 per cent cite word of mouth as their main influence when making a product choice, with advertising languishing far behind at just 15 per cent.
However, the report recommends that advertisers should consider word of mouth as an integral part of a campaign, rather than as an alternative, because ads drive it.
The agency has called those who drive word of mouth "transmitters". These people respond positively to marketing and take greater notice of advertising.
MEC has also identified several misconceptions about opinion formers.
The agency claims opinion formers are not an exclusive group of consumers, nor are they necessarily young and upmarket. Rather, they are defined by the category - if, for instance, they are experts on finance or heavy users of the category. They become opinion formers not because they buy eclectic brands but because they buy more than their contemporaries and are not marketing averse.