A SIMPLE METHOD FOR CENSORED AGE-OF-ONSET DATA SUBJECT TO RECALL BIAS- MOTHERS REPORTS OF AGE OF PUBERTY IN MALE TWINS

Genetic analysis of variation in age of onset of development milestone s or psychopathological behaviors has been little researched, owing la rgely to the computational difficulty of dealing with ''censored'' obs ervations. Censored observations arise when the only information on in dividuals is that they have reached a particular age but without onset having occurred. This paper shows how models can be simply fitted to such data using programs that can perform genetic analysis of categori cal data by maximum likelihood. The method is illustrated using the pr ogram Mr with data on maternal report of the onset of puberty in twin sons from the Virginia Twin Study of Adolescent Behavioral Development . Frequently, data on age of onset is collected by retrospective recal l. This can pose a variety of measurement problems. Suggestions are ma de for models that account for some of these problems or are robust to their presence. Substantial evidence for ''telescoping'' of onset dat es is found for the puberty data. If left unaccounted for, these effec ts can artifactually inflate estimates of common environment effects.