Continuity of care indices under an urn model

An urn model of Pólya-Eggenberger type is applied to the problem of measuring provider continuity in ambulatory care. The model is fitted to data from a Swedish community health care center, and predictions from the model are compared with observed counts from patients visit data. Two well known continuity of care measures, the COC and SECON indices, are shown to have a simple interpretation in terms of the model parameters, and their accuracy is discussed in the light of the urn model. Two further indices suggested in medical care literature are briefly discussed.