control group

(noun)

the group of test subjects left untreated or unexposed to some procedure and then compared with treated subjects in order to validate the results of the test

Related Terms

Examples of control group in the following topics:

  • Statistical Literacy

    • Two groups of rats were tested.
    • Both groups were injected with chemicals known to increase the chance of liver cancer.
    • The experimental group was fed saffron (n = 24) whereas the control group was not (n = 8).
    • Only 4 of the 24 subjects in the saffron group developed cancer as compared to 6 of the 8 subjects in the control group.
    • What method could be used to test whether this difference between the experimental and control groups is statistically significant?

  • Random Assignment of Subjects

    • Random assignment helps eliminate the differences between the experimental group and the control group.
    • Random assignment, or random placement, is an experimental technique used to assign subjects either to different treatments or to a control group (no treatment).
    • Consider an experiment with one treatment group and one control group.
    • If the experimenter were to assign all of the blue-eyed people to the treatment group and the brown-eyed people to the control group, the results may turn out to be biased.
    • If there are differences between the fertilized plant group and the unfertilized "control" group, these differences may be due to the fertilizer.

  • Randomization Tests: Two Conditions

    • The data in Table 1 are from a fictitious experiment comparing an experimental group with a control group.
    • The scores in the Experimental Group are generally higher than those in the Control Group with the Experimental Group mean of 14 being considerably higher than the Control Group mean of 4.
    • From Table 1 you can see that there are two rearrangements that would lead to a bigger difference than 10: (a) the score of 7 could have been in the Control Group with the score of 9 in the Experimental Group and (b) the score of 8 could have been in the Control Group with the score of 9 in the Experimental Group.
    • This means that if assignments to groups were made randomly, the probability of this large or a larger advantage of the Experimental Group is 3/70 = 0.0429.
    • Since only one direction of difference is considered (Experimental larger than Control), this is a one-tailed probability.

  • Statistical Controls

    • For example, during drug testing, scientists will try to control two groups to keep them as identical as possible, then allow one group to try the drug.
    • Negative controls are groups where no phenomenon is expected.
    • To continue with the example of drug testing, a negative control is a group that has not been administered the drug.
    • We would say that the control group should show a negative or null effect.
    • Positive controls are groups where a phenomenon is expected.

  • Case study exercises

    • To determine whether acupuncture relieves migraine pain, researchers conducted a randomized controlled study where 89 females diagnosed with migraine headaches were randomly assigned to one of two groups: treatment or control.43 patients in the treatment group received acupuncture that is specifically designed to treat migraines. 46 patients in the control group received placebo acupuncture (needle insertion at non-acupoint locations).
    • What percent in the control group?
    • Researchers studying the effect of antibiotic treatment for acute sinusitis compared to symptomatic treatments randomly assigned 166 adults diagnosed with acute sinusitis to one of two groups: treatment or control.
    • What percent in the control group?
    • Control: 2/46 = 0.04 → 4%.

  • The Salk Vaccine Field Trial

    • The responses of a treatment group of subjects who are given the treatment are compared to the responses of a control group of subjects who are not given the treatment.
    • The treatment groups and control groups should be as similar as possible.
    • The original design of the experiment called for second graders (with parental consent) to form the treatment group and first and third graders to form the control group.
    • In a double-blind experiment, neither the participants nor the researchers know which participants belong to the control group, as opposed to the test group.
    • Demonstrate how controls and treatment groups are used in drug testing.

  • Principles of experimental design

    • Controlling.
    • Researchers assign treatments to cases, and they do their best to control any other differences in the groups.
    • Researchers randomize patients into treatment groups to account for variables that cannot be controlled.
    • Randomizing patients into the treatment or control group helps even out such differences, and it also prevents accidental bias from entering the study.
    • For instance, if we are looking at the effect of a drug on heart attacks, we might first split patients in the study into low-risk and high-risk blocks, then randomly assign half the patients from each block to the control group and the other half to the treatment group, as shown in Figure 1.15.

  • What are Observational Studies?

    • An observational study draws inferences about the possible effect of a treatment on subjects, where the assignment of subjects into a treated group versus a control group is outside the control of the investigator.
    • This is in contrast with experiments, such as randomized controlled trials, where each subject is randomly assigned to a treated group or a control group.
    • In a hypothetical controlled experiment, one would start with a large subject pool of pregnant women and divide them randomly into a treatment group (receiving induced abortions) and a control group (bearing children), and then conduct regular cancer screenings for women from both groups.
    • Membership in this "treated" group is not controlled by the investigator: the group is formed after the "treatment" has been assigned.
    • In a controlled experiment, the investigator would randomly pick a set of communities to be in the treatment group.

  • The Portacaval Shunt

    • Numerous studies have been conducted to examine the value of the portacaval shunt procedure, many using randomized controls.
    • Of these studies, 63% were conducted without controls, 29% were conducted with non-randomized controls, and 8% were conducted with randomized controls.
    • In experimental design, random assignment of participants in experiments or treatment and control groups help to ensure that any differences between and within the groups are not systematic at the outset of the experiment.
    • Assign subjects with "heads" to one group, the control group; assign subjects with "tails" to the other group, the experimental group.
    • It provides control for all attributes of the members of the samples—in contrast to matching on only one or more variables—and provides the mathematical basis for estimating the likelihood of group equivalence for characteristics one is interested in.

  • Controlling for a Variable

    • There are also quasi-independent variables, which are used by researchers to group things without affecting the variable itself.
    • For example, to separate people into groups by their sex does not change whether they are male or female.
    • The essence of the method is to ensure that comparisons between the control group and the experimental group are only made for groups or subgroups for which the variable to be controlled has the same statistical distribution.
    • A common way to achieve this is to partition the groups into subgroups whose members have (nearly) the same value for the controlled variable.
    • Such analyses may be described as "controlling for variable $x$" or "controlling for the variations in $x$".