According to Chapter 8, Section 220.127.116.11 of the Medicare Program Integrity Manual, “sampling units are the elements that are selected according to the design of the survey and 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 sample designs, other types of clusters of payments may be used. In principle, any type of sampling unit is permissible as long as the total aggregate of such units covers the population of potential mis-paid amounts.”
In those 107 words, the Program Integrity Manual, which basically lays out the rules governing provider audits, tries to elucidate a very tenuous area of most audits, and that speaks to this: what is the appropriate unit to be audited? I have always had a problem with claim-level auditing, because in many cases, the claim itself is a composite of many different individual procedure codes. These can include codes for surgical, medical, E&M, radiological, supply, drug, and other types of services, procedures, and products.
In a recent audit in which I was a statistical expert, the Zone Program Integrity Contractor (ZPIC) chose to audit at the claim level. So they selected 47 claims at random and then audited the 227 individual lines within those claims. Some claims had only one procedure code, while others had up to 11. This was true of the sample, but the distribution of claim line frequency was different for the two. In fact, in the sample, the mean number of lines per claim was 4.2, and for the frame, it was 2.9. The problem here may not seem obvious, but it indicates that, in general, the claims for the sample are likely more complex than those for the frame.