noun 
1. 
regression  returning to a former state 


regress,
reversion,
retrogression,
retroversion 


reversal a change from one state to the opposite state; "there was a reversal of autonomic function"

2. 
regression  the relation between selected values of x and observed values of y (from which the most probable value of y can be predicted for any value of x) 


statistical method,
statistical procedure a method of analyzing or representing statistical data; a procedure for calculating a statistic



regression analysis the use of regression to make quantitative predictions of one variable from the values of another



statistics a branch of applied mathematics concerned with the collection and interpretation of quantitative data and the use of probability theory to estimate population parameters



linear regression,
rectilinear regression the relation between variables when the regression equation is linear: e.g., y = ax + b



curvilinear regression the relation between variables when the regression equation is nonlinear (quadratic or higher order)

3. 
regression  (psychiatry) a defense mechanism in which you flee from reality by assuming a more infantile state 


defence mechanism,
defence reaction,
defense mechanism,
defense reaction,
defence,
defense (psychiatry) an unconscious process that tries to reduce the anxiety associated with instinctive desires



psychiatry,
psychological medicine,
psychopathology the branch of medicine dealing with the diagnosis and treatment of mental disorders
