Thomas Burgess

Results 3 issues of Thomas Burgess

This PR adds a check to BaseFitter.summary, so it raises a ValueError if fit hasn't been run, and property checks won't fail for children like ParetoNBDFitter that lack members standard_errors_,...

Assuming these also should be converted like B-A.

The Bland-Altman plot can be done looking at the ratio A/B as an alternative to the difference A-B. We're plotting a=mean(X,Y) vs b=Y-X. In https://rdrr.io/cran/mcr/man/MCResult.plotDifference.html they also allow a=rank(X) a=sqrt(X*Y)...