I have a continuous dependent variable (scores on an exam) and a number of predictor variables that I'd like to use in a regression analysis, such as gender, age, and income. I'd like to convert age and income into categorical variables: low, medium, and high. I'd like to do this using percentiles, but am not sure if I should use tertiles (lower 33% = low, middle 33% = medium, upper 33% = high) or if I should divide the data into lower 25% (low), middle 50% (medium), and upper 25% (high).
Thoughts? Thank you!
Thoughts? Thank you!