What does it mean to say that a “statistically significant” effect was found?
Studies require the use of statistics when the outcome has a chance component to it. For instance, suppose we want to compare a drug treatment and a relaxation treatment as methods for lowering blood pressure. We administer the treatments to 100 people each, and find that one lowers blood pressure by 3 more than the other. Did that happen by chance, or was that method really superior? There would be a chance component to the results because individuals all respond differently, and even the same individual can have vastly different blood pressure readings depending on when and where the reading is taken. Statistical methods try to sort out the real differences from the chance variability. A difference or treatment effect is said to be statistically significant if chance alone would be unlikely to have produced it.
