Scientific control

The selection and use of proper controls to ensure that experimental results are valid (for example, absence of confounding variables) can be very difficult.

Controls are most often necessary where a confounding factor cannot easily be separated from the primary treatments.

If the treatment group and the negative control both produce a positive result, it can be inferred that a confounding variable is involved in the phenomenon under study, and the positive results are not solely due to the treatment.

In the drug testing example, we could measure the percentage of patients cured.

If the positive control does not produce the expected result, there may be something wrong with the experimental procedure, and the experiment is repeated.

If this information were to become available to trial participants, patients could receive a larger placebo effect, researchers could influence the experiment to meet their expectations (the observer effect), and evaluators could be subject to confirmation bias.

A blind can be imposed on any participant of an experiment, including subjects, researchers, technicians, data analysts, and evaluators.

During the course of an experiment, a participant becomes unblinded if they deduce or otherwise obtain information that has been masked to them.

Unblinding that occurs before the conclusion of a study is a source of experimental error, as the bias that was eliminated by blinding is re-introduced.

Meta-research has revealed high levels of unblinding in pharmacological trials.

[3] Blinding is an important tool of the scientific method, and is used in many fields of research.

Take identical growing plants ( Argyroxiphium sandwicense ) and give fertilizer to half of them. If there are differences between the fertilized treatment and the unfertilized treatment, these differences may be due to the fertilizer as long as there weren't other confounding factors that affected the result. For example, if the fertilizer was spread by a tractor but no tractor was used on the unfertilized treatment, then the effect of the tractor needs to be controlled.