An investigation of the false discovery rate and the misinterpretation of P values

The following proposition is justified from several different points of view. If you use P = 0.05 to suggest that you have made a discovery, you will be wrong at least 30 percent of the time. If, as is often the case, experiments are under-powered, you will be wrong most of the time. It is concluded that if you wish to keep your false discovery rate below 5 percent, you need to use a 3-sigma rule, or to insist on P value below 0.001. And never use the word “significant”.