Can an F-test be used in a regression that is quadratic, or can it only be used in a linear regression model? My regression I'm testing is quadratic but everything I've read about using F-tests state that it is used in a linear regression model.
Since your model is like
$$
Y = \alpha + \beta_1 X_1 + \gamma_1 X_1^2 + \beta_2 X_2 + \gamma_2 X_2^2 + \epsilon,
$$
it is still a linear model -- because it is linear in the terms. (&quot;Linear&quot; refers to the terms like $X_1$ and $X_1^2$ being linearly combined.)
You can use an $F$-test for your model.