Conclusion
We have reviewed the statistical analysis presented by your company to decide what causes group A to have higher income than the other groups. We conduced ANOVA tests, linear regression and decision trees. We agree with the analysis you have provided.
However, we have found that one important conclusion is not considered. Group A may have a higher income due to their time already spent in Country A. Yes, there is strong correlation between time of immigration to Country A and income. This does not mean that the policy should be changed. In fact, after further analysis we find that the other group’s income increases as the time in Country A increases.