Why Specify Experimental Design?
At level one of this topic, we introduced the two types of experimental design and at level two we explained the advantages of each. At this stage, we will explain why it matters which type of experimental design you choose. The key thing to remember is that the sample values collected in one sample of a paired design can paired with corresponding values in the other condition’s sample. This fact allows us to be much more specific when we make comparisons between the two conditions. In an independent experimental design, no pairings can be made so the best we can do is compare the average (the mean) of each group. Sampling Error and Variance You can understand the improved accuracy that a paired design provides by thinking about sampling error. Sampling error is likely to be far smaller when the same subject is measured twice. Here is an example. Imagine you measured your height on a monday morning, spent a week stretching, and measured your height again. Even the smallest change in he
