Why is there only one p-Value for the friedman test although it's a two way design
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like already in the title: i was searching for something like the 2 way anova but without the normal distribution requirement. the friedman test allows a two way layout but i only get 1 p-valie. but i want to know the impact of rows and column.
What am I misunderstanding? best regards
Shashank Gupta am 22 Apr. 2021
Friedman test in MATLAB as you pointed out give only one p-value which is associated with the column effect. Friedman effect cannot be used for interactions between the row and column factors. Although there are some workaround for separately finding out the p-values for row and column effect.
Test for column effect :-
p = friedman(x)
Test for row effect :-
% For data matrix with no replication, row effect can simply be done by
% taking transpose.
p = friedman(x');
% If the data matrix has replication then it is slightly complicated, below
% is one such template that can be done.
x = reshape(x, [3 2 3]); % First convert the data into 3 dimension data, with the first dimension representing the replicates
x = permute(x, [1 3 2]); % swapping the other two dimensions
x = reshape(x, [9 2]); % restoring the two-dimensional shape
p = friedman(x, 3);
I hope this helps.