The Impact of Sentencing Decisions about Similar Cases and Others' Opinion on Sentencing Decision

In 2009, Lay judge system started in Japan. Under this system, lay judges and professional judges determine guilty of criminals and sentences to the convicted criminals. After the determination of introduction of this system, some scholar have explored how that decision making is done by psychological experiments –mock trial study. However, the research which employed this method focuses on private lay judges’ decision, not outcomes after deliberation. It is due to the difficulty of conducting mock trial study with deliberation.

 Of course, the results of this research are useful when thinking about modification of trial procedure. However, the determination of sentences to the convicted defendants is not done privately, but is done through deliberation by lay judges and professional judges. In this paper, the impact of information which is given to lay judges is examined. In trials and sentencing deliberation, lay judges look graphs about past similar cases. This is basically shown in the form of graph of distribution, and it has powerful effect on lay judges’ sentencing decision. In a psychological experiment, the impact of that graph and participants’ opinion about how useful that graph is and how respectfully we should treat that graph are explored. In addition, there might be conflicting opinion with regard to sentencing outcomes by other lay judges. In the same experiment, reactions to those different opinions are also examined. This psychological experiment did not include sentencing deliberation itself, but due to that experiment, some important aspects about sentencing deliberation can be explored.

In this paper, the results of the psychological experiment are shown. Then, some practical implication about trial procedure is discussed based on the results. Especially, to incorporate general public opinion into judicial system is one of the goals of Lay Judge System in Japan. Therefore, the results are examined from this perspective.