Blood pressure after an operation

Use this diagram to show that a second factor can be varied in an experiment without affecting the accuracy of estimating the effect of the first factor (provided a factorial design is used).

Initially present this experiment as a completely randomised experiment with a single factor, the operation type (keyhole surgery or standard) since all patients get the same dose of drug. Repeat the experiment several times, accumulating the distribution of the estimated difference between the operation types.

Use the slider to vary the amount of a drug that is used (intended to reduce blood pressure) in a factorial design. Repeat the simulation and note that the accuracy of the estimated effect of the operation type is the same.

The diagram simulates an experiment to compare two operation types. The response variable is the systolic blood pressure of the patients two hours later.

A second factor, the dose of a drug that is intended to reduce their blood pressure after the operation, can also be varied.