Note this is a correlation analysis. Before draw any causal effect between the result and Developers' identity, the data itself may include bias.

To give an example of possible bias that totally not related to developers' identity. From Figure 3.9 and Figure 3.10, Softwipe scores over LoC have a very different pattern from star-repos, which could be:

If whether a developer uses swearwords is statistically independent, then a project with more contributors are more likely includes swearwords. More contributors may correlate with having a coding style guide which has causal effect on the score from SoftWipe tool (https://www.nature.com/articles/s41598-021-89495-8).

Be careful when trying to explain data :)