Objective: To describe the relationship of Mini-Mental State Exam (MMSE) scores and changes over time in MMSE scores to age and education in a population of older women.
Design: A prospective study of a defined population.
Setting: Various motherhouses and church-run health care facilities in the Eastern, Midwestern, and Southern regions of the United States.
Participants: Catholic sisters (nuns) participating in the Nun Study, a study of aging and Alzheimer's Disease. The 678 participants were 75 to 102 years old (mean 83.3, standard deviation 5.5, median 82.3) at the time of the first functional assessment. Second assessments were obtained an average of 1.6 years later on 575 survivors.
Measurements: The outcome variables were MMSE scores at the first assessment (Time-one), and MMSE scores at the second assessment (Time-two). The independent variables were age at Time-one, and education (bachelor's degree or no bachelor's degree).
Results: Time-one MMSE scores decreased with age at Time-one. The decrease in MMSE scores with age was less in sisters with bachelor's degrees than in sisters without bachelor's degrees. The changes in MMSE scores had a "U-shaped" relationship with Time-one score, where the greatest declines occurred in sisters with intermediate Time-one scores. Stratified analysis by age, education, and Time-one MMSE scores of 20 or greater because of the small numbers of sisters with Time-one scores less than 20. In sisters with Time-one MMSE scores in the categories 20 to 23, 24 to 26, or 27 to 30, older ages at Time-one were associated with greater decline in those with bachelor's degrees, but not in those without bachelor's degrees. Also, lower education was associated with greater decline in sisters aged 75 to 84 years at Time-one, but this education effect disappeared or reversed in sisters who were 85 years of age or older at Time-one.
Conclusions: Cognitive function as measured by the MMSE decreased with age at Time-one, most steeply as a function of age in those without bachelor's degrees. Cognitive function declined over 1.6 years within individuals, and the extent of decline increased with age in the sisters with bachelor's degrees. The extent of decline varied with age and education in an interactive manner, which may have been attributable to a hardy survivor effect in lower educated sisters. It may be necessary to consider such interactions whenever changes in function are studied, particularly when analyses are stratified by the initial level of function.