It means “return to(ward)”, with the implication that the observed difference from the mean is (partially) transient, so you’re returning to a past state.
Do you mean this in the context of statistics, or everyday life? My impression is that in the context of everyday life, it means to move down, but I could be mistaken.
Regarding the definition of “regress”, I mean in everyday life. I’ve never heard of it meaning “move down”, “decrease”, or “deteriorate” in a broad sense; I only know of it meaning that in the case I mentioned above, when the contextual assumption is that moving up or increasing has already been happening and is now being undone. In particular, a climb up one side of a hill of quality followed by a fall down a different side into a different worse state would not be a regression (though this can get blurry depending on which parts of the state are considered relevant).
However, because “regress” is used so commonly in that sort of context, the connotation of deterioration does exist, so you could make a reasonable case for the term “regression to the mean” being less clear than it could be on those grounds—that it pushes a default mental image of the deviating state being above or better than the mean, even though this is not an intended implication. It doesn’t mean “move closer” though—that’s derived entirely from the “to” part.
I think the implication of getting worse is strong enough that (outside the technical uses in statistics) you’d never say “regress” when the change involved wasn’t a worsening. E.g., if I try to imagine any of the following, I can’t see anyone actually saying them. “I have good news for you: the latest scans show that your cancer has regressed somewhat.” “The fifth wave of the COVID-19 pandemic is beginning to regress now.” “The most recent figures show some regression in the unemployment caused by last year’s financial crash.”
The statistical uses—“regression to the mean” and the practice of “regression” (meaning model-fitting), which historically is actually derived from “regression to the mean”—are of course well enough established that once you’re used to them they don’t carry any connotation of things getting worse.
[EDITED to add:] On looking in the OED, I find that in fact “regression” is used about tumours and the like. But I bet that in the unfortunate event that any of us has to consult an oncologist, they will not use the word in that sense with us; I think it’s for technical use only, just like the statistical sense.
Ah, this makes a lot of sense. Good examples. In looking at those examples, it does seem clear to me that my original impression about what it means in the context of everyday life was correct.
Do you mean this in the context of statistics, or everyday life? My impression is that in the context of everyday life, it means to move down, but I could be mistaken.
Regarding the definition of “regress”, I mean in everyday life. I’ve never heard of it meaning “move down”, “decrease”, or “deteriorate” in a broad sense; I only know of it meaning that in the case I mentioned above, when the contextual assumption is that moving up or increasing has already been happening and is now being undone. In particular, a climb up one side of a hill of quality followed by a fall down a different side into a different worse state would not be a regression (though this can get blurry depending on which parts of the state are considered relevant).
However, because “regress” is used so commonly in that sort of context, the connotation of deterioration does exist, so you could make a reasonable case for the term “regression to the mean” being less clear than it could be on those grounds—that it pushes a default mental image of the deviating state being above or better than the mean, even though this is not an intended implication. It doesn’t mean “move closer” though—that’s derived entirely from the “to” part.
I think the implication of getting worse is strong enough that (outside the technical uses in statistics) you’d never say “regress” when the change involved wasn’t a worsening. E.g., if I try to imagine any of the following, I can’t see anyone actually saying them. “I have good news for you: the latest scans show that your cancer has regressed somewhat.” “The fifth wave of the COVID-19 pandemic is beginning to regress now.” “The most recent figures show some regression in the unemployment caused by last year’s financial crash.”
The statistical uses—“regression to the mean” and the practice of “regression” (meaning model-fitting), which historically is actually derived from “regression to the mean”—are of course well enough established that once you’re used to them they don’t carry any connotation of things getting worse.
[EDITED to add:] On looking in the OED, I find that in fact “regression” is used about tumours and the like. But I bet that in the unfortunate event that any of us has to consult an oncologist, they will not use the word in that sense with us; I think it’s for technical use only, just like the statistical sense.
Ah, this makes a lot of sense. Good examples. In looking at those examples, it does seem clear to me that my original impression about what it means in the context of everyday life was correct.
I see. Thanks for clarifying.