"Maturity of thinking" of 15-year-old girls and boys as assessed from the reasons given for answers to questions about their beliefs

204 Finnish children (98 from the capital, 106 from a rural area) participated in a longitudinal study concerning the development of their world-view. In interviews carried out at age 15, subjects were asked to give reasons/grounds for their beliefs (attitudes, opinions). The reasons given for answers relating to 17 topics (e.g., life values, vocational intentions, beliefs about important topics in everyday life, global problems, and the experiential character of human life) were rated in terms of maturity of thinking (MOT) about that topic. The relaliability of the MOT sum scale was ≥0.90. MOT was unrelated to most the ability tests included, and to parents' standard of living, but was related to school achievement (including achievement 3 years later), teacher's ratings, subjects' reading and TV-watching habits and other information-seeking activities, and acceptance of "untraditional" values. It was also related to self-image variables in females but not in males. The possible preferability of ecologically valid topic in studies of maturity of thinking is discussed.