Dear Dr. Roach: In a recent column discussing the use of aspirin, you made reference to the results of a study that were neither statistically significant nor clinically meaningful. While I am quite familiar with the concept of statistical significance and believe it is very helpful in interpreting the results of a study, I am not familiar with the latter concept. Are you referring to a poorly designed study or one with too small of a sample? I am wondering whether clinically meaningful adds any benefit to the scientifically accepted concept of statistical significance. P.J.B.
Answer: Statistical significance is a concept central to understanding medical or other scientific studies. Often, one group (an experimental group, who may get a new treatment, for example) is compared with another group (the control group, who got some other treatment, usually the standard treatment or, if there is no standard treatment, a placebo). The difference in the outcome is looked at between the two groups.
A statistician employs one of several methods to calculate the likelihood that the difference between the two groups could have happened by chance, called the p-value. If the p-value is less than 5 percent, then that is usually considered statistically significant. The lower the p-value, the less the likelihood that the observed difference between the two groups could have happened by chance if the two treatments were identically effective.
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