A reliable instrument is one that is consistent in what it measures. If, for example, an individual scores highly on the first administration of a test and if the test is reliable, he or she should score highly on a second administration.
Imagine that you are conducting a study for which you must develop a test in mathematics for 7th-grade students. You develop a 30-point test and distribute it to a class of 12, 7th-grade students. You then administer the test again one month later to the day. The scores of the students on the two administrations of the test are listed below. Use Microsoft® Excel® or IBM® SPSS® to create a scatterplot with the provided scores, formatted as shown in the example graph. What observations can you make about the reliability of this test? Explain.