(a) Classification methodology.

(1) A patient classification system is used to classify patients in inpatient rehabilitation facilities into mutually exclusive case-mix groups.

(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) Data from admission assessments under §412.610(c)(1) are used to classify a Medicare patient into an appropriate case-mix group.

(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.

(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.

(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.

(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.

(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.

(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) Treatment patterns;

(2) Technology;

(3) Number of discharges; and

(4) Other factors affecting the relative use of resources.