The research was done by Dr. W. Murray Thomson of the School of Dentistry in Dunedin, New Zealand, and his colleagues in New Zealand and the United States. Dunedin is a city of about 120,000 in southern New Zealand. The subjects in the study include every baby born in Dunedin's only maternity hospital in a 12-month period beginning in 1972. The fact that more than 90 percent of the original cohort was available for study almost 30 years later suggests that this community is quite a stable one. However, that 20 percent of the cohort heavily smoked marijuana at age 32 suggests that Dunedin might not be quite the paradise its tourism Web sites suggest.