Measuring function for medicare inpatient rehabilitation payment

Health Care Financing Review, Spring, 2003 by Grace M. Carter, Daniel A. Relles, Gregory K. Ridgeway, Carolyn M. Rimes

RESULTS

Distribution of FIM[TM] Item Responses

Table 2 shows the mean and standard deviation of each of the 18 FIM[TM] items in our entire sample. For most items, the standard deviation is approximately 1.5--one-quarter of the six-point range of the item.

In order to use any functional measures in a payment system, we need to consider how formal and informal rules might affect patient classification. For example, items and scales for which many persons are placed at the bottom of the scale may be problematic because of the so-called floor effect--i.e., there may be real variation in the concept that the item or scale is attempting to measure that is not being captured. Similarly, a ceiling effect may conceal real variation at the top of the scale. In the FIM[TM] motor items (i.e., all but the last five items in the table), ceiling effects are apparently not a problem--eating is the item with the highest percentage of cases receiving the score of 7, and it is plausible that 40.9 percent of rehabilitation patients are, in fact, completely independent in eating. Similarly, it is plausible that 85.1 percent of rehabilitation patients are completely dependent at admission in going up stairs.

The remaining motor item with unusual data is transfer to tub or shower, where one-half of the patients were listed as completely dependent. On the surface, this appears strange, given that only 6.9 percent were completely dependent in transferring among bed and chair (or wheelchair) and only 12.2 percent in transfer to toilet. Based on informal conversations with hospital staff, we believe that a major reason for the high percentage of completely dependent scores on transfer to tub or shower is the UDSmr rule that, when an activity is not observed, then it is to be coded as 1 (completely dependent). This rule was formulated under the belief that the predominant reason why one of these 18 items was not observed would be because it was dangerous for the patient to try it. Such is completely plausible with the stairs item, for example. However, in discussing the transfer to tub rule with hospital staff, we found that many hospitals provide the patient with only sponge baths during the first 3 days of the stay; showers and tub baths are postponed until later in the stay. For such hospitals, the score of 1 in transfer to tub says nothing about the capability of the patient to perform this activity, and therefore nothing about the length or intensity of rehabilitation required.

The cognitive items individually show a potential for a ceiling effect. Given the complexity of cognitive functions such as comprehension and expression, we cannot rule out the existence of a real ceiling effect from this data. Of course, even if there are cognitive levels of expression and memory that are not captured by the items, these may have little to do with resources required for rehabilitation.

Table 3 shows the mean value of the motor score minus the transfer to tub item and of the cognitive score for each RIC. Theoretically, the motor score varies from a 12 to 84. There is substantial variation across RICs, with the average motor score varying from 41.4 for traumatic brain injury to 49.8 for pulmonary patients. Low average values of the cognitive score are found only in stroke and brain injury RICs. There are a substantial number of cases at the cognitive ceiling in all other RICs.