本文使用二部負二項分配模型，將民眾在全民健保制度下的就診，區分為機率及頻率兩部分，並依照總就診次數及西醫、牙醫、中醫三類就診數，分別分析其影響因素，以修正現有文獻的缺失。結果發現，除了健康狀沿對就診機率及頻率皆有影響外，其餘變數的影響力，則有所差異。年齡主要影響民眾的就診頻率，所得則影響就診機率，部分負擔以及就醫距立也只對民眾的就診頻率有顯著的影響力。可見將二者分開探討有其必要性。此外，由於三類門診的性質不同，影響因素也不一樣，僅以門診總就診次數進行迴歸分析，研究民眾的醫療需求，可能會發生高估或低估因素影響力的情形。改善的方法，應以三類門論取代門診總數，作為個別研究對象較為合宜。

　　　　　A Two-Part Negative Binominal distribution (Two-Part NegBin) model is used in this study to analyze the decision to utilize outpatient care under National Health Insurance (NHI). The decision making process is separated into two parts: the contact analysis and the frequency analysis. The empirical results show that most factors have inconsistent impacts on the contact and frequency decisions except for the health conditions. For example, age affects an individual's contact decision; however, copayments and distance affect his (her) frequency decision. The different empirical outcomes between the contact and frequency decisions support the formulation of two decision processes in the outpatient care utilization instead of adopting one-step decision process. Meanwhile, since outpatient care includes three different types of services, which are Western medicine, dentistry, and Chinese medicine, we divide total outpatient visits into three categories in the analysis of the demand for outpatient care. In order to avoid biased estimations and to provide more precise policy implications, it is more appropriate to separate the three categories of services in analyzing patients' utilization behaviors.