I am doing a regression analysis on the various factors which influence accident levels in my city. The 2 factors used in my regression model are covariates :
urbanization level of the city and,
percentage of persons buying cars within the past year in the city.
From my regression analysis, both showed significant positive association with my outcome variable.
However, when I presented my regression model, one of my colleagues mentioned that my analysis, i.e., the impact of the 2 covariates on the dependent variable could be flawed and does not reflect reality since I have left out an important covariate such as the
number of alcohol outlets/pubs in the city. What statistical reasoning can I rebuttal his argument with? I am not quite sure what to make of his argument and if it is even valid. Suggestions/discussion are welcome. Cheers.