42 CFR §412.620

1. (a)Classification methodology.
   1. (1)A patient classification system is used to classify patients in inpatient rehabilitation facilities into mutually exclusive case-mix groups.
   2. (2)For purposes of this subpart, case-mix groups are classes of Medicare patient discharges by functional-related groups that are based on a patient's impairment, age, comorbidities, functional capabilities, and other factors that may improve the ability of the functional-related groups to estimate variations in resource use.
   3. (3)Data from admission assessments under § 412.610(c)(1) are used to classify a Medicare patient into an appropriate case-mix group.
   4. (4)Data from the discharge assessment under § 412.610(c)(2) are used to determine the weighting factors under paragraph (b)(4) of this section.
2. (b)Weighting factors—(1) General. An appropriate weight is assigned to each case-mix group that measures the relative difference in facility resource intensity among the various case-mix groups.
   1. (2)Short-stay outliers. We will determine a weighting factor or factors for patients that are discharged and not transferred (as defined in § 412.602) within a number of days from admission as specified by us.
   2. (3)Patients who expire. We will determine a weighting factor or factors for patients who expire within a number of days from admission as specified by us.
   3. (4)Comorbidities. We will determine a weighting factor or factors to account for the presence of a comorbidity, as defined in § 412.602, that is relevant to resource use in the classification system.
3. (c)Revision of case-mix group classifications and weighting factors. We may periodically adjust the case-mix groups and weighting factors to reflect changes in—
   1. (1)Treatment patterns;
   2. (2)Technology;
   3. (3)Number of discharges; and
   4. (4)Other factors affecting the relative use of resources.