Dichotomania is an obsessive compulsive disorder to which medical advisors in particular are prone… Show a medical advisor some continuous measurements and he or she immediately wonders. “Hmm, how can I make these clinically meaningful? Where can I cut them in two? What ludicrous side conditions can I impose on this?” (S. Senn)
Like this shredder, converting a continuous variable into a categorical one is a popular and reliable way to destroy information.
Dichotomization of continuous information tends to encourage dichotomous thinking, this limits the research questions we can ask and the conclusions we’re able to draw. There is a literary canon decrying this practice written by statisticians (unfortunately it seems it is only read by statisticians). See Suggested Reading below…
Breaking Up is Hard to Do: The Heartbreak of Dichotomizing Continuous Data
The Cost of Dichotomising Continuous Variables
Why Carve Up Your Continuous Data?
Dichotomizing Continuous Predictors…a bad idea
The Cost of Dichotomization