Statistics for diagnostic procedures. II. The significance of "no significance": what a negative statistical test really means.

Statistical tests are often used to compare two or more groups. When the tests show "no significant difference," many authors/readers conclude that this means that the groups are identical. Often this outcome is merely the result of inadequate sample size. The adequacy of sample size depends on well established mathematical principles, not on the investigator's intuition. The real meaning of "no significant difference" is discussed.