# Difference between R² and Chi-Square

The question is in the title: In both cases I use R² and Chi-Square to test if a fit/model is good enough. Up to now I only know that R² is used for models (?) and Chi-Square for Fits/functions (?). Is this true? And how exactly do they differ? Thank you!

• The answer to this would almost amount to a complete introductory statistics course. Can you narrow it down a bit to a specific scientific analysis where you are in doubt what to do? – mdewey Aug 1 '17 at 12:52
• I'm just learning these two terms because I always stumble over them. And it confuses me. Also what's the difference between max likelihood and chi-square.. for me they are all doing the same and it's a bit hard to separate them (for me). – Ben Aug 1 '17 at 12:56

## 1 Answer

Found this after a quick google: "R^2 is used to quantify the amount of variability in the data that is explained by your model. It's useful for comparing the fits of different models.

The Chi-square goodness of fit test is used to test if your data follows a particular distribution. It's more useful for testing model assumptions rather than comparing models."

sounds like Chi-square is more useful if you have a function you are trying to test (or a model you are trying to fit to your data) as opposed to the R^2 which tells you how much variability there is in your data, and therefore how much the best model fits.

• Thanks! So that's my assumption :) But thanks anyway! Of interested is now how/why they are applied to different cases respectively in which way they work differently. – Ben Aug 1 '17 at 13:07