Senile dementia of the Alzheimer type. Subject attrition and testability in research
J. Botwinick, M. Storandt, L. Berg and S. Boland
Department of Psychology, Washington University, St Louis, MO 63130.
There are inherent methodologic problems in investigating senile dementia
of the Alzheimer type (SDAT) but this study indicated that, with regard to
behavioral test measurement, some of the obvious problems are partially
mitigated. First, these data showed that the progressive decline seen in
longitudinal SDAT studies is of the same type and magnitude seen in
cross-sectional comparisons. Thus, comparing SDAT groups differing in
severity provides for the same observations as following up subjects with
mild SDAT over time. This study also demonstrates that with certain kinds
of tests, selective subject attrition may not be any greater in
longitudinal investigations than found in normal aging research. Subjects
who dropped out of the longitudinal study were not that different from
those who remained in, at least in terms of initial test performance on
challenging tests. In this study less than 5% of the subjects with SDAT
originally classified as being in the mild stage of the disease remained in
this stage after 6 3/4 years of investigation. This inexorable downward
path of the subject with SDAT is what appears paramount. Given the
similarity of staging in longitudinal and cross-sectional studies, prior
test performance levels in the latter studies can be ascertained even if
with less accuracy than in longitudinal studies.
