Experiments, Placebos, and Effect Size (a parable)

The purpose of this experiment was to measure the effects of wording on people's behavior.

Method

Participants were randomly assigned to three groups, two experimental and one control. Participants were payed $5 to participate in this experiment and were told that it would only take five minutes of their time, and then were sent into a room with an experimenter who introduced himself and handed participants their instructions.

Participants in the first experimental condition were handed a sheet of paper that said, "Please complete as many push ups as you can without stopping."

Participants in the second experimental condition were handed a sheet of paper that said, "Please complete as many sit ups as you can without stopping."

Participants in the control condition were handed a blank sheet of paper.

Results

Participants in the first experimental condition completed on average 10.4 push ups (median 8). They completed on average 0 sit ups (median 0).

Participants in the second experimental condition completed on average 22.8 sit ups (median 24). They completed on average 0 push ups (median 0).

Participants in the control condition completed on average 0 push ups (median 0) and 0 sit ups (median 0).

Conclusion

This experiment found with high probability (p < 0.05) that people's behavior is affected by the wording of instructions they are given.