F or no F: a summary

[Alain de Cheveigne <alain@xxxxxxxxxxxxxxxxxxx>]

Thanks to all those that responded!  I've condensed the responses into a
summary, hopefully without perverting their meaning too much.

My query was whether the conventional F-value, degrees of freedom and
p-value triplet could acceptably be summarized by the p-value alone. My
concern was to cut down detail to make things easier to read.

The consensus is "leave them in!".  The main reasons are:

a) Useful redundancy.  The degrees of freedom (more than the F-value) give
information about the experimental design that might not be clear
otherwise.  To make things that clear in the text would require so much
explanation as to defeat the original purpose of improving readability.
b) They help check that the author knows what he's doing.  One journal
editor said that half of papers submitted contain errors, such as improper
ANOVA models, that can be caught by considering the dfs.
c) The F-value and the degrees of freedom allow an indirect estimate to be
made of the size of the effect relative to the population variance.
d) Convention.  Everyone reports them, and expects them to be there.
Upsetting the reader by breaking the rules also defeats the purpose of
readability.

Some people added that they'd like to see still more information: means and
standard deviation for each condition, and even some indication of the
shape of the distribution, such as histograms, so the reader can be sure
that the assumptions behind the analysis are valid.

Others objected to the practice of reporting post-hoc p-values.  A given
level of significance should be chosen from the start, and adhered to, and
results should be reported in YES-NO format.  Meaning, I suppose, that only
the F-value and degrees of freedom are reported for each effect.

Someone objected to the practice of reporting F and p values with lots of
digits: "instead of saying F = 51.4 surely F = 50 would  suffice".

Finally a few agreed that if all necessary information about the design is
well described elsewhere, then even the p-values can be omitted (assuming
the results meet the proper level of significance).

Many of the answers were very clear and carefully written.  It seems a
shame to not reproduce them.  If the authors agree, I'll make a compilation
and post it in another message.

Thanks again!

Alain