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

Figure 1 shows the distribution of the motor score minus the transfer to tub item for stroke and lower extremity joint replacement. There is almost a normal distribution in each RIC, but the stroke cases have a much larger standard deviation. Unlike the motor scores, the shape of the cognitive score distribution depends strongly on RIC (Figure 2). There is much more variation across cases in the stroke RIC.

[FIGURES 1-2 OMITTED]

Relationship Between Individual FIM[TM] Items and Cost

Table 4 shows the regression log of cost on each FIM[TM] item and age for each of six large RICs. For the range of values found in the table, the coefficient gives a good estimate of the percent increase in cost with an increase in one level of independence in the FIM[TM] scale. For example, the -0.030 coefficient on the eating item within the stroke RIC says that, all other responses and age equal, an increase of 1 in the eating item score results in a 3-percent drop in the expected cost of the case. The t-statistic shows the accuracy of the measurement of the coefficient with a t-statistic with an absolute value of 2.0 or greater providing confidence that the coefficient is not 0 or of opposite sign from that shown here (statistically significantly different from 0 at p < 0.05).

Table 5 counts the coefficients from the regressions on all 21 RICs by their sign and range of value of t. Although the individual item effects are measured less precisely in the smaller RICs, the same items tend to have high likelihoods of the expected negative relationship between cost and independence and statistically significant t-statistics in both Tables 4 and 5.

Table 4 shows that in all six RICs there are substantial and significant decreases in cost with increasing independence in 7 of the 13 FIM[TM] motor items (eating, dressing lower body, toileting, bladder management, transfer to bed or chair, transfer to toilet, locomotion). The same is true in five of the six RICs for two additional items (bathing and stairs). Table 5 shows that each of these 9 items was negative in between 17 and 21 of the regressions, and only stairs exhibited any positive and statistically significant coefficients.

One motor item, transfer to tub or shower, has consistently positive effects--costs increase with increasing independence. This is probably due in part to the overcoding of complete dependence, as previously discussed. However, it also may be due to the mixture of tub and shower in the same item and to the use of different types of assistive devices. For example, it may be that a patient who can transfer to a tub bench would need assistance in transferring to a shower seat. Thus, the transfer to tub/shower item provides only a situational measure of the person's capabilities rather than an absolute measure. If patients with more capability were given harder situations at admission, this would help explain the positive and significant relationship between cost and transfer to tub or shower.

The remaining three motor items--bowel management, dressing upper body, and grooming--appear to predict cost in some RICs, but not in others. Although we do not understand this completely, it may be relevant that bowel management, transfer to tub/shower, and dressing upper body had the lowest reliabilities of any FIM[TM] items in a recent study (Buchanan et al., 2002).