A great deal of information is available from the baseline evaluation in this study and the crosssectional analyses that can be done with these data will be very valuable. There are, however, limitations in what we can learn from cross-sectional data. The baseline data revealed many relationships between factors that were studied and disability, but there may be circularity in these relationships that cannot be sorted out if we only have cross-sectional data available. For example, abnormalities in certain biomarkers may be a cause of disability or may be caused by disability. Only by doing longitudinal analyses that begin with non-disabled persons can the temporal sequence be determined. Cross-sectional analyses only permit the study of factors that are currently related to disability while longitudinal analyses allow for the identification of subclinical markers of risk that predict future disability onset. There is therefore much to be gained by performing a follow-up evaluation of the cohort to obtain longitudinal data.