A researcher would like to compare two methods for teaching math to third-grade students. Two third-grade classes are obtained for the study. Mr. Jones teaches one class using method A, and Mrs. Smith teaches the other class using method B. At the end of the year, the students from the method-B class have significantly higher scores on a mathematics achievement test. Does this result indicate that method B causes higher scores than method A? Explain your answer, and identify the general problem that precludes a cause-and-effect explanation.

Although this study might suggest that method B causes higher scores than method A, this cannot be absolutely determined. This is because there are many factors that are involved in this experiment and are not accounted for. For example, we do not know if one class was already getting better results before the implementation of this method. If that was the case, it would suggest that the results could be attributed to the differences between the teachers, or the differences between the students. The general problem that precludes a cause-and-effect explanation is that we do not have a way of determining which factor is the one that made the difference with the students.