The Sampling Unit

8.4.3.2.2 - The Sampling Unit (Rev. 11962; Issued: 04-21-23; Effective: 05-22-23; Implementation: 05-22-23) Sampling units are the elements that are selected based on the chosen method of statistical sampling. They may be an individual line(s) within claims, individual claims, or clusters of claims (e.g., a beneficiary). For example, possible sampling units may include specific beneficiaries seen by a physician during the time period under review, or claims for a specific item or service. In certain circumstances (e.g., multi-stage sampling designs), other types of clusters of payments may be used. Certain sampling theorems require an assumption that sampled items are “identically and independently distributed” (iid). In sampling from a finite universe without replacement, there is always a certain amount of dependence because the probability of selection changes with each unit that is selected. However, correlations of characteristics in the target population do not imply dependence in sampling. Sampling units may be correlated because they come from the same location, the same provider/supplier, the same time period, or any number of other reasons. In this context, independence means the selection of one sampling unit does not influence, or gives no information about, the outcome of another selection. Overpayments are not random variables. They are fixed values, though unknown prior to sampling. Therefore, regardless of any correlation that may exist between sampling units, the outcome, or overpayment, of any particular unit does not change based on the outcomes of other units. Unlike procedures for suppliers, overpayment estimation and recovery procedures for providers/suppliers and non-physician practitioners who bill Part A MACs, in a non-PPS environment, must be designed so that overpayment amounts can be accurately reflected on the provider’s cost report. Therefore, sampling units must coincide with an estimation methodology designed specifically for that type of provider/supplier to ensure that the results can be placed at the appropriate points on the cost report. The sample may be either claim-based or composed of specific line items. For example, home health cost reports are determined in units of “visits” for disciplines 1 through 6 and “lower of costs or charges” for drugs, supplies, etc. If claims are paid under cost report, the services reviewed and how those units link to the provider/supplier’s cost report must be known. The contractor shall follow the instructions contained in section 8.4 et seq., but use the projection methodologies provided in Pub. 100-08, Exhibits 9 through 12, for the appropriate provider type. Pub. 100-08, Exhibits 9 through 12, are to be used only for claims not paid under PPS.