Even If the Research Hypothesis Is True, an Experiment May

Even if the research hypothesis is true, an experiment may not produce significant results because:

A) sampling error and other uncontrolled variables may cause too little variance in the population
B) the sample that happens to be selected from the population being studied may not be extreme enough to provide a clear case for rejecting the null hypothesis
C) the original population is very extreme with regard to its mean and standard deviation, leading the researcher to prove the null hypothesis
D) just as there is a probability of rejecting the null hypothesis, there is always a chance that it must be accepted