Question

when can I use non parametric alternative test: the Wilcoxon signed rank test.?

instead of t-test

Answer 1

Sol:

if the assumption of normality is violated for the paired t test use the wilcoxon signed rank test.

the test requires the ordinal scale of measurement.

the observations must be related or dependent.

steps for the test:

compute the differences between related observations.drop observations with 0 difference from the sample.

rank the absolute differences from low to high.

return the signs to the ranks and sum positive and negative ranks.

compare the smaller of the two rank sums with the t value obtained from table.