I have a continuous & categorical outcome variables in three groups of patients, where the groups are defined by time periods 2010-2011, 2012-2014, 2015-2016. I found out that age and gender are confounding variables for income, and therefore, I wish to make the age distribution of the 3 groups constant so that any difference in income cannot be attributed to age. Same as gender.
I don't think regression analysis works since we have a categorical variable (the 3 groups), but I'm just clueless. Any advice on how I should go about doing this?