What other differences exist?
One variable you didn't consider in your earlier statistical test is job level. Different job levels tend to have different pay levels, so if the mix of job levels for new hires is different than the mix of job levels for current employees, you could be dealing with omitted variable bias.
Check whether the job level composition is the same for new hires as it is for current employees.
This exercise is part of the course
HR Analytics: Exploring Employee Data in R
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
# Load package
___
# Create a stacked bar chart
___