Stability is important because it allows us to obtain the same results with repeated measurement using the same person and the same instruments for reliability from one time to another. Therefore, if I had to design an instrument in which a private, for profit school would be able to evaluate the quality and value of its variety of curricula and courses I would ensure that the instrument has stability by doing an observational study of the same students who are participating in the test. Then those students would be observed a second time to determine reliability. The text states that it is often possible to do more than one observational study of the same subject and then compare them to see if they are consistent. However situational factors do sometimes change that can alter the observation (Cooper & Schindler, 2008).

Equivalence is a perspective on reliability that relates to variations at one point in time among observers and samples of items (Cooper & Schindler, 2008). Therefore, to test equivalence, I would use the instrument with more than one group of students, but at the same time. Different groups of students at the same time. Thus, I would be able to determine equivalence is to compare the scores of different observers for the same study. Equivalence is more concerned with how a set of items will categorize an individual. Thus if there are differences in responses between students, but if they are classified the same the test is said to be of good equivalence (Cooper & Schindler, 2008). Thus the equivalent instrument should be good at knowing the differences between students of all the groups.

Internal consistency is another approach to reliability that uses one administration of