Reliability of an instrument can greatly affect the level of error. More reliable less error, less reliable more error. Therefore, scores or values of your sample are only estimates of the population. This is important. Because these scores are only estimates of a population, we can explain differences in results and why a treatment may work one time and not work any more.
Researcher randomly selects samples from each and finds the mean of each group.
Perhaps, but remember we must take into account sampling and measurement error. Because of error, it is generally more acceptable to conclude that there is no real difference between the two groups. This is referred to as the null hypotheses . It is also referred to as a statistical hypothesis , especially in the context of probability of sampling and measurement error. Alternatively, there is the research hypothesis which is also called the alternative hypothesis .