Types of Repeated Measure Designs

Crossover Studies

• Crossover studies are the most popular type of repeated design experiment because all subjects in the study receive the same treatments, making it easier to compare. The study works by administering one group of subjects experiment X and another group experiment Y. The first group is then tested with experiment Y while the second is tested with experiment X. The problem with crossover studies is the possibility of carryover effects where the first test influences the second.

Longitudinal Studies

• A longitudinal study includes many observations of the same group of subjects over a long period of time, sometimes decades. They are used to study developmental trends over time. For example, Harvard Medical School conducted a heart health study with the citizens of Framingham, Massachusetts to determine how lifestyle effects heart health over a long period of time. The drawback is that they had no control group.

Panel or Cohort Studies

• Panel or cohort studies observe a specific group of individuals. They are a form of longitudinal studies but focus on people specifically rather than any scientific phenomena. They focus on the life histories of the people involved and try to find casual relationships for the outcomes observed. In addition, most of the people, or cohort, have a common characteristic.

Power

• Repeated measure designs can be quite powerful because they reduce the natural variation of having many test subjects. This increases the confidence level with the results of studies. However, it is harder to extract the results onto the larger population. The population can also become used to the experiment over time and thus naturally adapt their practices to succeed at the experiment.