̷ ̷ˈgreshən noun
( -s )
Etymology: Latin regression-, regressio, from regressus (past participle of regredi to go back) + -ion-, -io -ion
1.
a. : an act or the fact of regressing : regress , retrogression , reversion
b. : a hypothetical reversal of direction in a biological evolutionary process that is sometimes invoked to explain the extinction of the graptolites and similar paleontologic phenomena
2. : a trend or shift toward a mean or toward a lower or less perfect state (as of function or differentiation): as
a. : apparent trend of offspring in respect to heritable characters away from specializations exhibited by their parents and toward the mean development characteristic of their biotype
b. : a functional relationship between two or more correlated variables that is often empirically determined from data and is used especially to predict values of one variable when given values of the others
the regression value of y on x is linear
specifically : a function that yields the mean value of a random variable under the condition that one or more independent variables have specified values
c. : a gradual spontaneous diminution or fading of a latent or developed photographic image
d.
(1) : progressive decline (as in size, severity, or intensity) of a manifestation of disease
marked regression of a tumor often follows radiation
regression of symptoms followed the climax
(2) : gradual loss of specific differentiation and function by a body part especially as a physiological change accompanying aging
menopausal regression of the ovaries
e.
(1) : reversion in behavior, thinking, attitudes, or identifications to an earlier mental or behavioral level or to an earlier stage of psychosexual development in response to organismic stress or to suggestion — compare fixation
(2) : gradual loss of memories and acquired skills (as in old age) in which the order of development is reversed so that the most recent memories are lost first and the earliest acquisitions are the last to go
3. : retrograde motion especially of an astronomical orbital characteristic