Design of Experiments > Experimental Group An experimental group [sometimes called a treatment group] is a group that receives a
treatment in an experiment. The “group” is made up of test subjects [people, animals, plants, cells etc.] and the “treatment” is the variable you are studying. For example, a human experimental group could receive a new medication, a different form of counseling, or some vitamin supplements. A plant
treatment group could receive a new plant fertilizer, more sunlight, or distilled water. The group that does not receive the treatment is called the control group.What is an Experimental Group?
- You are testing to see if a new plant fertilizer increases sunflower size. You put 20 plants of the same height and strain into a location where all the plants get the same amount of water and sunlight. One half of the plants–the control group–get the regular fertilizer. The other half of the plants–the experimental group–get the fertilizer you are testing.
- You are testing to see if a new drug works for asthma. You divide 100 volunteers into two groups of 50. One group of 50 gets the drug; they are the experimental group. The other 50 people get a sugar pill [a placebo]; they are the control group.
- You want to prove that covering meat prevents maggots from hatching. You put meat into two different jars: one with a lid and one left open. The jar with the lid is the experimental group; the jar left open is the control group. [This is the famous Redi experiment].
The only difference between the control group and the experimental group must be the hypothesis you are testing. In the first example above, the people must be of similar age, health status, socioeconomic background etc. That way you know that if the drug improves asthma for the experimental group, it’s not due to other factors like better health status or a younger age.
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For a Linux kernel feature governing computing resources, sometimes known as a hypothesis groups, see cgroups.
In the design of experiments, hypotheses are applied to experimental units in a treatment group.[1] In comparative experiments, members of a control group receive a standard treatment, a placebo, or no treatment at all.[2] There may be more than one treatment group, more than one control group, or both.
A placebo control group[3][4] can be used to support a double-blind study, in which some subjects are given an ineffective treatment [in medical studies typically a sugar pill] to minimize differences in the experiences of subjects in the different groups; this is done in a way that ensures no participant in the experiment [subject or experimenter] knows to which group each subject belongs. In such cases, a third, non-treatment control group can be used to measure the placebo effect directly, as the difference between the responses of placebo subjects and untreated subjects,[3][4] perhaps paired by age group or other factors [such as being twins].
For the conclusions drawn from the results of an experiment to have validity, it is essential that the items or patients assigned to treatment and control groups be representative of the same population.[5] In some experiments, such as many in agriculture[6] or psychology,[7][8][9] this can be achieved by randomly assigning items from a common population to one of the treatment and control groups.[1] In studies of twins involving just one treatment group and a control group, it is statistically efficient to do this random assignment separately for each pair of twins, so that one is in the treatment group and one in the control group.[clarification needed]
In some medical studies, where it may be unethical not to treat patients who present with symptoms, controls may be given a standard treatment, rather than no treatment at all.[2] An alternative is to select controls from a wider population, provided that this population is well-defined and that those presenting with symptoms at the clinic are representative of those in the wider population.[5] Another method to reduce ethical concerns would be to test early-onset symptoms, with enough time later to offer real treatments to the control subjects, and let those subjects know the first treatments are "experimental" and might not be as effective as later treatments, again with the understanding there would be ample time to try other remedies.
Relevance[edit]
A clinical control group can be a placebo arm or it can involve an old method used to address a clinical outcome when testing a new idea. For example in a study released by the British Medical Journal, in 1995 studying the effects of strict blood pressure control versus more relaxed blood pressure control in diabetic patients, the clinical control group was the diabetic patients that did not receive tight blood pressure control. In order to qualify for the study, the patients had to meet the inclusion criteria and not match the exclusion criteria. Once the study population was determined, the patients were placed in either the experimental group [strict blood pressure control