A shoe manufacturer wanted to determine which type of material, "Material X" or "Material Y," to use on the soles of their shoes to get maximum wear. Twenty teenage boys wore one shoe with each type of sole. For each young man, a coin was tossed; if heads, "Material X" would go on the right shoe and "Material Y" on the left. If tails, "Material X" would go on the left shoe and "Material Y" on the right. After wearing these shoes four months, the thickness of the sole of each shoe was measured. What type of study is this?

A matched pairs design is a specific type of randomized block design, that lessens variability from individual differences. It´s effective when the research has only two optional conditions, and subjects can be assorted into sets of two, with a blocking variable. Within each pair, the different materials are randomly distributed.

This is a matched pairs experiment because there are two measures noted in each boy: the right sole is paired with the left one, so ware can be compared, but variations in wear from one boy to another is removed from the experimental error.