Advertising affects buyer attitudes to the brand in a number of characteristic ways. The important effects are similar across product types fmcg, durables and services because brand attitude formation is relatively similar in the unpressured environments where most advertising is received. Attitudes change in correlated patterns in response to advertising, and can be used to explain most changes in preference for the brand. This allows pretesting to show both whether and how advertising is working, and with a relatively high degree of confidence. The practice of pretesting must embrace five principles to be effective; marginal buyer preference, comprehensive attributes, attribute importance, competitive effects and correlated attributes. This allows the problems of quantitative pretesting that have been experienced in the past by users to be largely resolved.