Other studies have documented the relationship between adolescents' high school achievement and academic-related characteristics and their likelihood to attend and complete college. In an analysis of predictors of college degree completion, Adelman (1999) followed the sophomore cohort of High School and Beyond study until they were age 30. Sample sizes varied by outcome examined as data were not complete for each variable, but all analyses appeared to include at least 3,000 respondents. In a model including only pre-college and family background controls, academic competence and course-taking behavior during high school, which was measured as a composite variable that made up of test score on the mini, enhanced SAT test, class rank and GPA, and curricular rigor or number of credits completed in intense, academic courses and courses commonly required by colleges, such as foreign language and higher level math and science, was found to be the strongest predictor of college completion. Marsh (1991b) also found course-taking behavior, ability, being in the academic track, and GPA to be independently predictive of college attendance. These findings held after controlling for background factors.