If the null hypothesis is true then the findings from the study are the result of chance or random factors. Difference between the outcomes from a sample of the population and the true value obtained from looking at the outcomes from the entire population. Statistical methods are used to estimate the probability that chance alone accounts for the differences in outcomes. In most clinical trials, a result is statistically significant if the difference between groups could have occurred by chance alone in less than 1 time in 20. Clinical significance has little to do with statistics and is a matter of judgment.
Studies can be statistically significant yet clinically insignificant.
Otherwise known as the probability of Type I error. The measured probability of a finding occurring, i.e. rejecting the null hypothesis, by chance alone given that the null hypothesis is actually true. The probability of detecting an effect in the treatment vs. control group if a difference actually exists. Must also specify the size of the difference. Mistakenly rejecting the null hypothesis when it is actually true.