SIR – You mentioned research which revealed that shoppers often prefer “50% extra free” to a notionally more generous 30% reduction in price, and you cited this as evidence of irrationality or poor mathematical ability on the part of consumers (“Something doesn’t add up”, June 30th). I think you may be wrong and consumers may be right.

There is, as the advertising sage Jeremy Bullmore observed, a significant difference between a bonus and a bribe. A price tells you much more about a product than merely what it costs. A price cut may be sensibly perceived as a mark of mild desperation on the part of the seller and it is not unreasonable to infer from a price cut that a product is an inferior good. Charging the full price but adding something extra does not convey the same desperation.

In any case this whole debate is silly. If people value 50% extra free more highly than 33% off, then that is an end of the matter. Since all value is subjective, what you are doing by offering the former is simply creating more perceived value at a lower cost. Whether or not the resulting behaviour conforms to some autistic neoclassical idea of rationality is irrelevant. If the sole purpose of life was to be rational, we would have banned golf years ago.

Rory Sutherland
Vice chairman Ogilvy & Mather UK