Formula reference—t-test, Pearson, Spearman and degrees of freedom

Use the supplied formula for the selected test and calculate degrees of freedom where required.

The final step is a decision about significance and biological meaning, not just a number.

A Pearson coefficient near +1 indicates a strong positive linear association under valid conditions; it does not prove one variable causes the other.

Do not choose a test because its formula is familiar; choose it from the data type and question.