INTRODUCTION

For decades, scholars and practitioners have been frustrated by the very limited capacity of either psychological or marketing models to predict individual choices on particular occasions. This paper discusses a theory which explains the degree to which the extant models omit important influences that produce varied individual choice behaviour. The focus of this paper is on the sequences of product purchases. Discretionary actions and activities are also covered.


THE THEORETICAL AND APPLIED RELEVANCE OF VARIED BEHAVIOUR

The assumption that consumers make rational, utility-maximizing choices has played an important role in economic thought. As long as preferences remain unchanged, the consumer is expected to choose the most preferred of the available products. Thoughts about consumers’ behaviour towards substitutes hold a similar position. If a consumer’s preference for the most preferred alternative product declines or the product is currently unavailable, the consumer is expected to choose a close substitute. From the firm’s strategic point of view, this means that the marketer of a secondary brand should make its brand similar to the most popular brand.

Careful consideration of the preceding description of consumer choice behaviour and the firm’s selection of a strategy immediately leads one to question the general applicability of these assumption / thought. Although consumers often display stable preferences, sound choice behaviour seldom remains constant. Instead, consumers frequently change their choices of products or brands. Furthermore, the choices made on different occasions often involve two very different products or brands. In summary, changing, varied behaviour is the rule. Managers often avoid the use of simple "me-too" brands, recognizing that consumers are seeking more than simple substitutes. This tendency is seen directly in a number of product categories in which successful products are seldom replaced with highly similar products. Instead, a degree of product newness is viewed as being essential to maintain consumer interest.

The theory of consumer choice behaviour that is presented in this paper is designed to explain the typical degree of variability that consumers exhibit in a series of related choices. Should this theory more accurately describe individual choices, than the meaning and predictive power of many models must be questioned. For example, the results from all preference-based mapping methods, such as MDPREF (Carroll, 1972) and the Schonemann-Wang (1972) models, should be interpreted with great care. In these cases, the analyst must resist jumping to the conclusion that the choice objects that appear close to each other have similar characteristics. All simple attribute-based choice models, such as the widely used conjoint method, must also be interpreted carefully. Here one must resist the assumption that the set of most preferred items will necessarily have similar characteristics. Typically, the set of most preferred or most frequently chosen products will contain items that are very different. These products do not necessarily satisfy the notion that the objects’ attributes will surpass the total utility produced. For example, sometimes a consumer may want a cold beverage and at other times the same consumer may want a hot beverage. Furthermore, the more of one kind of beverage that an individual consumes, the less likely the consumer will make the same choice on the next occasion. Unlike the reasons that produce constant-purchase and / or constant-use behaviour, different motives produce changes in purchase and use. To predict the choice made on the next occasion, one needs to account for the consumer’s prior choice behaviour.
A THEORY OF VARIED CONSUMER BEHAVIOUR

Psychologists have long recognized that individual judgements and choices contain an important random element that leads to inconsistent behaviour. Thurstone’s Law of Comparative and Categorical Judgement modelled individual judgements and choices. The random component present in most contexts of interest to marketing professionals include larger variables that are too costly to measure or for which practical measurement methods have not been developed. Consider the purchase of breakfast cereal. At the point of purchase, a favourite brand may be out of stock, the customer may be distracted, the shopper’s child may make the selection, or a clerk restocking part of the assortment may contain choice. Although this list contains only a few of the conditions which can affect consumer choice, it demonstrates the difficulty of observing and recording all of the relevant influences. All unmeasurable influences are labelled inexplicable causes of varied behaviour.

There are two important types of explicable