Formulation of an index of propensity to buy

James Rothman
Sales Research Services Ltd.

INTRODUCTION

In marketing a non-durable consumer product, we need to do two things: we need to reduce the number of buyers of the product who cease to buy it to a minimum, and we need to persuade as many people to start buying the product as possible. This latter necessity makes it important in market research to be able to identify potential buyers of a product.

In fact, of course, it is impossible to classify a person as being either a potential buyer or not, since in most cases we are faced with a continuous gradation from those with very favourable attitudes to the product at one end of the scale, down to the people who have a strong prejudice against it and are very unlikely to buy it in the future, at the other. Consequently, instead of speaking of potential buyers, it is probably more realistic to measure propensity to buy and to speak of people with a high or low propensity to buy a product. The concept of propensity or predisposition to buy is not a new one. It is, however, generally used loosely and, although questions are included in surveys which purport to give some indication of it, this is usually done with reservations as to the validity of the questioning technique.