**Density function of
the central F distribution**: In the absence of a treatment effect, the
observed ratio of treatment to error mean squares follows the

where *p* and *q* are the model test and error degrees of freedom respectively, and the beta
function The
area under the density function above *F* is the probability of making a Type-I error in rejecting a true null hypothesis.
The critical *F*_{[α]} is the value of *F* when this
probability = *α* (often at *α* = 0.05).

Doncaster, C. P. & Davey, A. J. H. (2007) *Analysis of Variance and Covariance: How to
Choose and Construct Models for the Life Sciences*. Cambridge: Cambridge
University Press.

http://www.southampton.ac.uk/~cpd/anovas/datasets/