Question

Why do we need to consider more than one basis for comparison?

Answer 1

In statistics, the multiple comparisons, multiplicity or multiple testing problemoccurs when one considers a set of statistical inferences simultaneously[1]or infers a subset of parameters selected based on the observed values.[2] In certain fields it is known as the look-elsewhere effect.

The more inferences are made, the more likely erroneous inferences are to occur. Several statistical techniques have been developed to prevent this from happening, allowing significance levels for single and multiple comparisons to be directly compared. These techniques generally require a stricter significance threshold for individual comparisons, so as to compensate for the number of inferences being made.