Logistic and cart modeling of decline in functional status

Wu J, Rosen AK, Berlowitz DR, Kazis LE, Ash AS, Moskowitz M. Logistic and cart modeling of decline in functional status. Paper presented at: VA HSR&D National Meeting; 1999 Feb 1; Washington, DC.

The importance of initial functional status (FS) in predicting future FS has been clearly demonstrated in the literature. However, there is little consensus on how to use activities of daily living (ADLs), categorically or continuously, in modeling FS. This study compares several approaches to using initial FS to model decline in FS. Our sample consists of 16,998 residents who resided in VA long-term care facilities for any time from 4/1/96 (or later) up to 10/1/96. The Patient Assessment File (PAF) was used to evaluate the changes in residents' FS. Baseline FS was measured using 3 ADLs: eating, transferring, and toileting (each rated on a 1-5 scale). Decline in FS was defined as an increase (worsening) of two or more in the summed score (ADLSUM) of eating, transferring, and toileting between baseline and semi-annual assessments. Patient characteristics related to decline (e.g., age, medical conditions, and length of stay) were used as risk factors along with baseline ADLs, to predict decline in FS. Logistic regression models were developed using each of the 3 ADLs as well as ADLSUM and an additional ADL, mobility. Variables were modeled both continuously and categorically. We also developed a classification tree (using CART), based on ADLSUM and each of these 4 ADLs. The regression R2s ranged from 0.042 to 0.059, while the c-statistics ranged from 0.66 to 0.69. The model that used categorical groupings from CART produced the highest R2 and c-statistic. We found that decline in FS was not linearly associated with baseline ADLs. Therefore, models that use ADLs categorically or those that use ADLSUM quadratically may be more appropriate in predicting future FS. Variation in model performance indicates that caution must be taken to capture the complexity of the relationship between initial FS and decline in FS.