  In software project management, risk management is a critical factor. Project
managers use existing lists of risk or perform brainstorming to identify the
risks. However, it is not easy to perceive all the risks objectively. As a
result, some risks are perceived based on subjective impression, which leads to
risk biases. So, our goals are (i) We clarify the risk perception of developers
to enhance the reliability of the brainstorming, and (ii) we calibrate the risk
assessment based on a mathematical model to make more accurate risk list. In
the analysis, we collected data concerning the risk perception of 69
professional software developers via a questionnaire. The average number of
years of experience among these professionals was 18.3. Using the dataset, we
applied factor analysis to clarify the factors that affect the evaluation of
risk impact. The questionnaire was based on the risk perception theory
established by Slovic, in which "dread" and "unknown" are the major factor of
risk perception. The analysis result shows that (i) risk experience (i.e.,
whether a developer actually faced the risk or not) sometimes affects risk
assessment (evaluation of risk impact), (ii) risk perception is considered to
be based on unknown and dread factors, and (iii) risk assessment can be
calibrated by a mathematical model (the average absolute error was 0.20).
