Scientific control

controlcontrolscontrolledcontrolled experimentcontrol groupexperimental controlnegative controlcontrol groupscontrolled experimentscontrolled study
A scientific control is an experiment or observation designed to minimize the effects of variables other than the independent variable.wikipedia
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Experiment

experimentalexperimentationexperiments
A scientific control is an experiment or observation designed to minimize the effects of variables other than the independent variable.
Experiments typically include controls, which are designed to minimize the effects of variables other than the single independent variable.

Scientific method

scientific researchscientificmethod
Scientific controls are a part of the scientific method.
Experiments should be designed to minimize possible errors, especially through the use of appropriate scientific controls.

Placebo

placebo effectplacebosplacebo studies
Some improvement is expected in the placebo group due to the placebo effect, and this result sets the baseline which the treatment must improve upon. 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.
In drug testing and medical research, a placebo can be made to resemble an active medication or therapy so that it functions as a control; this is to prevent the recipient or others from knowing (with their consent) whether a treatment is active or inactive, as expectations about efficacy can influence results.

Observer-expectancy effect

experimenter effectobserver effectexpectancy bias
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.
It is a significant threat to a study's internal validity, and is therefore typically controlled using a double-blind experimental design.

Sham surgery

shamsham-operatedsham-operated group
In some cases, sham surgery may be necessary to achieve blinding.
In clinical trials of surgical interventions, sham surgery is an important scientific control.

Bias

biasesunbiasedbiased
Blinding is the practice of withholding information which may bias an experiment.
It is usually controlled using a double-blind system, and was an important reason for the development of double-blind experiments.

James Lind

LindLind, James
Although Lind was not the first to suggest citrus fruit as a cure for scurvy, he was the first to study their effect by a systematic experiment in 1747.

Controlling for a variable

controlcontrollingaccounted for
In controlled experiments of medical treatment options on humans, researchers randomly assign individuals to a treatment group or control group.

Clinical trial

clinical trialsclinical studiesclinical study
Lind conducted the first systematic clinical trial in 1747.

Observation

observerobservationsobserved
A scientific control is an experiment or observation designed to minimize the effects of variables other than the independent variable.

Dependent and independent variables

dependent variableindependent variableexplanatory variable
A scientific control is an experiment or observation designed to minimize the effects of variables other than the independent variable.

SDS-PAGE

SDS-polyacrylamide gel electrophoresisSDS PAGEpolyacrylamide gel electrophoresis
Many controls are specific to the type of experiment being performed, as in the molecular markers used in SDS-PAGE experiments, and may simply have the purpose of ensuring that the equipment is working properly.

Sugar substitute

sweetenerartificial sweetenersweeteners
For example, if a researcher feeds an experimental artificial sweetener to sixty laboratory rats and observes that ten of them subsequently become sick, the underlying cause could be the sweetener itself or something unrelated.

Rat

ratsgiant ratSpecies of rat
For example, if a researcher feeds an experimental artificial sweetener to sixty laboratory rats and observes that ten of them subsequently become sick, the underlying cause could be the sweetener itself or something unrelated.

Confounding

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

Test validity

validityvalidvalidation
Positive controls are not used to assess test validity.

Sensitivity and specificity

sensitivityspecificitysensitive
For example, to assess a new test's ability to detect a disease (its sensitivity), then we can compare it against a different test that is already known to work.

Enzyme assay

enzyme activityactivityspecific activity
Similarly, in an enzyme assay to measure the amount of an enzyme in a set of extracts, a positive control would be an assay containing a known quantity of the purified enzyme (while a negative control would contain no enzyme).

Standard curve

For example, in the enzyme assay discussed above, a standard curve may be produced by making many different samples with different quantities of the enzyme.

Observational error

systematic errormeasurement errorsystematic bias
While this does not ensure that there are no differences between the groups, it ensures that the differences are distributed equally, thus correcting for systematic errors.

Crop yield

yieldyieldscrop yields
For example, in experiments where crop yield is affected (e.g. soil fertility), the experiment can be controlled by assigning the treatments to randomly selected plots of land.

Soil fertility

fertilefertilityfertile soil
For example, in experiments where crop yield is affected (e.g. soil fertility), the experiment can be controlled by assigning the treatments to randomly selected plots of land.

Confirmation bias

Backfire effectdisconfirmation biasconfirmation
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.