I'm looking for open freely available data sets related to software development quality: code quality, defect rates, comparison across programming languages. Where/how can I find such data sets?
Here are a few sources to take a look through:
Most comprehensive and closest to what I think you're looking for is a project by the acronym of PROMISE (PRedictOr Models In Software Engineering). Go to http://promisedata.googlecode.com/svn/trunk/defect/ to go straight to their data which is organized by code base and into CSVs. For example, tomcat.csv. It looks like the project also has a number of tools to help analyze and create models from the data.
Eclipse Bug Data! is, as it sounds, a project to mine bug and version datas from the Eclipse project.
NASA also publishes "cleaned versions of publicly available NASA MDP software defects data sets" over at http://nasa-softwaredefectdatasets.wikispaces.com/
EDIT: there are also a number of academic papers on this topic that you might want to skim to see if they reference specific data sets or sources.
Note: This answer only covers a particular aspect of code quality.
OpenHub (ex Ohloh) contains 666,192 projects and mentions for each one:
- The number of comment lines
- The total number of lines
- The programming language used (or proportions if several used)
So, you can use that data to compute the comment/code ratio for many programming languages.