  Open Source Software (OSS) has been a popular form in software development.
In this paper, we use statistical approaches to derive OSS quality estimation
models. Our objective is to build estimation models for the number of defects
with metrics at project levels. First CATREG (Categorical regression with
optimal scaling) is used to obtain quantifications of the qualitative
variables. Then the independent variables are validated using the stepwise
linear regression. The process is repeated to acquire optimal quantifications
and final regression formula. This modeling process is performed based on data
from the OSS communities and is proved to be practically valuable.
