I am trying to guide students towards the correct statistical tests in biology. I found the decision tree attached at https://dzchilds.github.io/stats-for-bio/choosing-models-and-tests.html and have added some text in red as I am trying to understand if there are some errors / omissions in it - or if I am misunderstanding some of the tests.
I have 4 main questions questions (you can see in red text in the graphic the matching locations by number):
The Wilcoxon (signed rank) test is listed in two places. Would it be correct to also say the Sign test could be applied in the situations given, but that the Wilcoxon (signed rank) test is preferred?
The t-test is listed in three places. However, would the z-test not also be an option? My understanding is that if we are working with comparing ratios/proportions we should not use the t-test but use the z-test instead. Additionally, I see recommendations that if we have 30 or more samples we should use z-test instead of the t-test. If what I just said is correct, then this graphic should show z-test as an option at all 3 locations that t-test is shown? If I am not correct, how would z-tests be incorporated correctly into this decision tree?
Near the bottom they list the Kruskal-Wallis test. I believe this chart neglects the Friedman test option, which could be added by adding another branching question about whether the samples are related (paired) or independent (unpaired). This would guide students to choose the Friedman test for related (paird) samples and the Kruskal-Wallis test for independent (unpaired) samples. If I am wrong about this, where would the Friedman test be shown in this chart?
The chart does not include the F-test, which I think based on how it is organized would be better addressed by adding a 4th question about whether they are looking at a difference in variances or not. Does that make sense as the chart is organized, or would it fit within the existing questions somehow?