Adopting the premise that "Indian" is a socially and politically constructed mutable concept, this thesis examines the implications of amendments to the legislative definition of Indian for the quality of Registered Indian vital statistics. In 1985, Bill C-31 introduced significant changes to the registration provisions of the Indian Act. The implications of population growth and compositional changes resulting from Bill C-31 for demographic and epidemiologic rates have not been addressed in the literature. This study compares 1980 through 1991 Registered Indian data for a sample of six Manitoba bands to distinguish differentials in compositional variables over time and across residence divisions and model these effects upon demographic and epidemiologic rates. The principal methodologies employed include direct standardization of mortality rates, life table analysis of mortality, and deterministic analysis of fertility and reproduction. These analyses reveal an increased proportionate contribution of the off-reserve population to the total band population over time, substantial decreases in standardized mortality rates, increases in life expectancy, particularly for off-reserve females, and decreases in off-reserve measures of fertility and reproductive success. The observed trends and differentials are attributed mainly to increases in population without commensurate increases in mortality and fertility during the study period. The results of these analyses demonstrate off-reserve and total band data to be significantly flawed for the 1985 to 1991 period.