Market research uses more and more sophisticated methods of data collection and statistical analysis procedures, in order to forecast the product preferences and buying patterns of potential customers. These methods include conjoint ana­lysis and particularly the discrete choice analysis. Respondents have to choose between different product concepts several times. It is possible to select one or even none of the concepts. Based on the choice or no-choice, it is possible to derive the market potential which a particular product concept may provide.

This naturally assumes that people behave as they have stated. The invalidity of this assumption is evident in studies which show, that often only a significant mi­nority of those who express a purchasing intention will actually make a purchase. Accordingly, product potential is significantly overestimated in these cases.

The following questions are of vital importance to enable a more valid estimation:

What is the relationship between an intention to purchase at the time of the survey and the purchasing behaviour at a later date? Which reasons were decisive if the behaviour deviated from the stated intention?

ln order to answer these questions a longitudinal study as well as a large sample are required. Online access panels are the ideal method for this purpose, as those surveyed can be obtained at a relatively low cost while at the same time providing a high response rate, even in a test-retest measurement. Furthermore,

respondent data can be used for pre-selection of defined target groups. In Janu­ary 2006, 802 panel participants were surveyed with regard to their purchasing intentions in two product categories (credit cards and flat screen TVs) (purchase within 6 mo nth s). Six months later a second survey was made with the same test sample.

The results of the study indicate that the type of interrelationship between the purchasing intention and an actual purchase depends on the product category. This can be referred to different reasons not to purchase in the categories. Whe­reas there is frequently a deferral in the purchase of a flat screen TV, the planned purchase is waived with credit cards (particularly where the purchase of a second credit card was the intention).