Behavioral economics have provided various insights to decision making problems for the last decades. In this article, I briefly introduce a few of the researches that are applied or applicable to healthcare and clinical decision making problems. In the last section, I also highlight the ideas of Nudge for behavior changes. The topics include the probability weighting and the S-shaped value function in Prospect Theory, the ambiguity aversion, and the cognitive biases such as framing effect, confirmation biases, and overconfidence.

The decision makings under uncertainty have been thoroughly researched and analyzed by formal models. At the same time, there have been many reported anomalies or "irrational behaviors" in the literature, which simply contract with those formal models. To incorporate the irrational behaviors, the researchers have also developed and modified the existing models. The Prospect Theory is definitely one of the most successful modifications. It is consist of two main components, the probability weighting function and the S-shaped value function. These functions combined together offer the broader framework that can explain several well-known anomalies, and they enable us to analyze the source of the irrationality in the clinical decision makings.

The psychology researches identify numerous forms of cognitive biases. We must be aware of those systematic tendencies of biases within our own decision makings, before we start debates over whether some decisions are rational or irrational, whether they are justifiable or not, and whether they are correct or wrong. Although it is still difficult for us to correct our unconscious biases at the site, it is important to understand the tendency of cognitive biases to prevent us from repeating any similar mistakes, if any, in the future. For this purpose, I select confirmation bias and overconfidence to write about.

Lastly, the concept of "nudge" is highlighted. A nudge is a behavioral science oriented method of guidance toward behavior changes. For instance, when an authority wants to make people do vaccinations, it can request or require them to do so, or subside for vaccinations. Instead, a simple letter that asks people to decide when to take the vaccination successfully worked. While requests, requirements and subsidies are active and explicit interventions, the nudge is rather passive and implicit and it is effective, too. There are varieties of nudges that are applicable to healthcare. I introduce a couple of examples to show the great potential of nudges in this field.

本稿では、2012年度に実施された一般名処方の推進を含むジェネリック医薬品に対するインセンティブ政策に着目し、政策の経済効果を明らかにすることを目的にする。分析を通じて、次の3点が明らかとなった。（1）本政策を通じて、ジェネリック医薬品の販売量は降圧剤市場で7.7％程度押し上げられ、特に病院、診療所でのジェネリック医薬品の利用が拡大された。（2)都道府県別に分析したところ、ジェネリック医薬品の利用のみならず、政策の効果についても地域差が存在した。政策の効果と過去のジェネリック医薬品の利用状況は正の相関関係にあり、2012年度以前からジェネリック医薬品を積極的に利用していた地域ほど、政策の効果が大きい傾向にあることが確認された。（3）先発医薬品からジェネリック医薬品への切り替え時における患者属性の違いを考慮に入れて2012年度に行われた政策の財政効果を試算したところ、降圧剤市場全体に費やされる薬剤費の1％強（年間120億円程度）が抑制されたことが明らかとなった。この結果は、患者属性の異質性を考慮しない場合よりも3割以上高い抑制額であり、患者属性の違いを考慮しない従来の方法に基づく数値は過小となっている可能性が指摘された。さらに、インセンティブ政策への政府の追加支出額は30.4億円と試算され、実質的な薬剤費抑制効果は87.6億円となった。