Both Uses

regress
in
Flowers for Algernon -- Short Story
(Edited)

I've got to find the reason for the sharp regression in Algernon.
p. 17.2

regression = return to a former (less advanced) state
As I review the records and data on Algernon, I see that although he is still in his physical infancy, he has regressed mentally.
p. 17.9 *

regressed = returned to a former (less advanced) state

Definitions:

(1) (regress as in: regressed instead of progressed)
to go backward or return to an earlier, less advanced state
(2) (regress as in: regressed income on education)
use mathematics or statistics to find the relationship between different variables
(3) (meaning too rare to warrant focus)
Specialized definitions of regression include:
- tax policy: regressive taxes cost the poor more relative to their income than the rich
- psychology: go back to more childish behavior
- parapsychology: return in one's mind to a previous life (usually under hypnosis)
- logic: reasoning from conclusion to evidence