A.1.9—Statistical tests

A statistical test compares data with a null expectation. Choose it from the variable type, paired or unpaired design, distribution and question—not from the result you hope to obtain.

State the null hypothesis, identify the test assumptions and report the test statistic or probability with a conclusion about the null. Keep biological importance separate from statistical significance.

A before-and-after treatment on the same organisms is paired; independent groups need a different comparison. A correlation question is not answered by a two-group test.

A significant result does not prove causation or guarantee a large effect.