The utilization of outpatient care services involves two steps of sequential decisions. The first step decision is about whether to initiate the utilization and the second one is about how many more visits to make after the initiation. Presumably, the initiation decision is largely made by the patient and his or her family, while the number of additional visits is decided under a strong influence of the physician. Implication is that analysis of the outpatient care utilization required to specify each of the two decisions underlying the utilization as a distinct stochastic process.
This paper is concerned with the number of physician visits, which is, by definition, a discrete variable that can take only non-negative integer values. Since the initial visit is considered in the analysis of whether or not having made any physician visit, the focus on the number of visits made in addition to the initial one must be enough. The number of additional visits, being a kind of count data, could be assumed to exhibit a Poission distribution. However, it is likely that the distribution is over-dispersed since the number of physician care utilization employed an analysis based upon the assumption of a negative binomial distribution which is a type of overdispersed Poission distribution. But there is an indication that the use of Poission distribution making adjustments for over-dispersion results in less loss of efficiency in parameter estimation compared to the use of a certain type of distribution like a negative binomial distribution.
An analysis of the for outpatient care utilization was performed focusing on an assessment of appropriateness of avaliable techniques. The data used in the analysis were collected by a community survey in Hwachon Gun, Kangwon Do in 1990. It was observed that a Poisson regression with adjustments for over-dispersion is superior to either an ordinary regression or a Poisson regression without adjustments for over-dispersion. In conclusion, it seems the most approprite to assume that the number of physician visits made in addition to the initial visits exhibits an over-dispersed Poisson distribution when outpatient care utilization is studied based upon a model which embodies the two-part character of the decision process underlying the utilization.
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