Assessment of the relevance of ethnographic studies, and especially of the importance of the research focus, is even more open to uncertainty and disagreement than assessments of their validity. Perhaps the most common contribution claimed for ethnographic studies, however, is that they fill a gap in the literature, in the sense of dealing with a phenomenon about which there has been little previous research. An example of criticism of research for failing to make a contribution to our knowledge can be found in some comments on a study of 'patter merchants', market traders who engage in an elaborate 'spiel' which attracts an audience and persuades some of its members to buy the goods on offer. As with the assessment of validity, assessment of the relevance of a study is a matter of judgement; and, even more obviously than in the case of validity, it can involve disagreement.