David is a marketer for a U$.$S$.$ mobile phone company. He is analyzing the demographic data collected about the German market, which the company will enter soon. As he plans the marketing mix strategy for rollout, he see that a wide range of Germans currently have mobile phones. David assumes that most Germans use mobile phones the same way people in the U$.$S$.$ do and that teenagers also have phones, when in fact most do not. David$$s assumption illustrates which cautionary area marketers need to watch out for with demographics?