The first two chapters relate offending to some attribute of the offenders. The first reviews the association between offending and mental test scores, and the second compares the association between offending and being hospitalized with a psychiatric diagnosis. The third and fourth chapters both analyze the relation between age and offending. The third article applies and expands a Markov model used in 1972 by Wolfgang and his associates, and analyzes the probabilities of offending in a two-year period given the criminal record for the previous two-year period. It further questions whether the transition matrices of probabilities change with age. In the fourth chapter, a detailed analysis of the age structure of offenders and the variations of offenses with age are studied. The four studies presented here make basic use of the longitudinal character of the project. 1 appendix, 10 notes, 4 figures, 38 tables, 82 references, 5 matrices. (Author abstract modified)