I have been writing a research proposal. In a particular part of the proposal, I talk about statistical methods that will be used to avoid "overfitting." This is a statistical concept describing a situation in which a model is overly complex and therefore has low error but not because of real signal but because of the large number of variables in the model. (See Wikipedia link: https://en.wikipedia.org/wiki/Overfitting)

A friend commented that she thought it should be "over fitting". This is probably where the term "overfitting" came from.

I wanted to pose this question to the Stack Exchange English Language & Usage to get people's thoughts on the matter! Which spelling should it be, "over fitting" or "overfitting"?

  • 2
    Google Books shows a wider usage of "overfitting" vs "over fitting" in statistical/mathematical contexts: books.google.com/ngrams/…
    – user66974
    Apr 26 '17 at 18:18
  • I have seen 'overfitting' a lot, 'over-fitting' also quite a bit, but 'over fitting' much less.
    – Řídící
    Apr 26 '17 at 18:22
  • 4
    Please include the research you've done (on the accepted spelling variant/s). Apr 26 '17 at 22:14

In the statistical context, you want to avoid overfitting. (I have not seen it written as over fitting in any of my graduate Economics or Statistics classes (graduated in Dec 2016). And a Google search for "over fitting" will direct you towards the more popular "overfitting.")

I searched for "overfitting" at scholar.google.com and found about 193,000 results. (One title is Stopped training and other remedies for overfitting).

Some have written it "over-fitting" (On over-fitting in model selection and subsequent selection bias in performance evaluation).

One can also find "over fitting" (Pseudomathematics and financial charlatanism: The effects of backtest over fitting on out-of-sample performance).


is traditionally defined as training some flexible representation so that it memorizes the data but fails to predict well in the future.

I would suggest that you (tongue planted firmly in cheek):

  1. Write "overfitting" for an academic context.
  2. Draft it as "over fitting" when your girlfriend can see it.
  3. Choose another term (e.g., "We sought a parsimonious model.")
  4. Seek appropriate relationship counseling.
  • Quite tongue in cheek, but thanks - very helpful!
    – M. Warden
    Apr 27 '17 at 15:27

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