To investigate prospects for enrollment decline, institutional researchers from Michigan's 15 public universities participated in an enrollment project grounded in detailed examination of headcounts and credit hours over time. Each institution reported enrollment for 12 fall terms (1974 through 1985) categorized by age group, gender and degree level (baccalaureate, first professional, graduate). The data were aggregated and used in conjunction with state demographers' cohort population estimates to compute enrollment rates and average credit hour loads for 66 student subgroups, and the effect on enrollments of a changing population profile (fewer 18- to 24-year olds and more older people) was isolated. This phase produced an estimate that population shifts would cause systemwide headcounts to decline by 11% between 1985 and 2000, while credit hours would drop by 13%. A multiple regression model was tested that was design to relate the enrollment behavior or various age-sex-degree level groups to variations in income, unemployment, tuition and financial aid. Although the limited number of observations mandated cautious interpretation, sensitivity to the economy and college costs clearly varied considerably from one subgroup to another. Alternate projections were generated using two models. Data are presented in four tables and a figure. Contains 9 references. (Author/KM)