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Matched Pairs Design
A matched pairs design is a special case of a
randomized block design.
It can be used when the experiment has
only two treatment conditions; and subjects can be grouped
into pairs, based on some blocking variable. Then, within each
pair, subjects are randomly assigned to different treatments.
The table to the right shows a matched pairs design for a hypothetical
medical experiment, in which 1000 subjects each receive one of two
treatments - a
or a cold vaccine. The 1000 subjects are grouped into 500
matched pairs. Each pair is matched on gender and age.
For example, Pair 1 might be two women, both age 21. Pair
2 might be two men, both age 21. Pair 3 might be two women, both age 22;
and so on.
For this hypothetical example, the matched pairs design is an improvement
completely randomized design.
Like the completely randomized design, the matched pairs design
uses randomization to control for confounding. However, unlike
the other design, the matched pairs design explicitly controls for two potential
variables - age and gender.