4 A study of young adults investigated the validity of self- reported dental agenesis (DA) using a guided questionnaire. The responses were then compared with childhood dental records and radiographs

(Baelum et al. 2011). Of the 176 respondents with documented evidence of DA, 155 (88%) self- reported DA. Of the 117 respondents with no documented evidence of having DA, 110 (94%) reported the absence of DA.

(i) Defi ne sensitivity and specifi city in general terms.

(ii) Interpret these defi nitions in the context of this study.

(iii) This sample was deliberately drawn to include a high proportion of young adults with recorded dental agenesis. If the true prevalence of DA in the population is 7%, what are the implications for self- reported DA as a population- screening tool for the actual occurrence of DA in an individual?