But can you be absolutely (which is pretty darn) sure? No, you cannot. Why? First, because you can never be sure that you are testing a sample that identically reflects the profile of the population. And even if the sample perfectly represents the population, there are always other influences that might affect the outcome and that you inadvertently missed when designing the experiment. There’s always the possibility of error (another word for chance). By concluding that the differences in test scores are due to differences in treatment, you accept some risk. This degree of risk is, in effect
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