It is very common to categorise people, especially in the advertising business. Also traditional marketing theory has taken in consumer segments as a favorite topic. Segmentation is closely related to the broader concept of classification. From a historical point of view, classification has its origin in other sciences as for example biology, anthropology etc. From an economic point of view, it is called segmentation when specific scientific techniques are used to classify consumers to different characteristic groupings. What is the purpose of segmentation? For example, to be able to obtain a basic understanding of grouping people. Advertising agencies may use segmentation totarget advertisements, while food companies may usesegmentation to develop products to various groups of consumers. MAPP has for example investigated the positioning of fish in relation to other food products and analysed possible segments in the market. Results show that the statistical model used identified two segments - a segment of so-called "fish lovers" and another segment called "traditionalists". The "fish lovers" are very fond of eating fish and they actually prefer fish to other dishes. The traditionalists are characterised by favouring pork, poultry and beef. Since it is difficult to change consumers' tastes, the short-term consequence may be to focus on the "fish lovers" and target the communication towards these consumers. In the long run, "traditionalists" may be persuaded to revise their evaluation of fish - for example by focusing on quality. Therefore, taking heterogeneity between segments into account makes a lot of difference, quantitatively as well as qualitatively.