The true experiment is often thought of as a laboratory study. However, this is not always the case. A true experiment is defined as an experiment conducted where an effort is made to impose control over all other variables except the one under study. It is often easier to impose this sort of control in a laboratory setting. Thus, true experiments have often been erroneously identified as laboratory studies.
To understand the nature of the experiment, we must first define a few terms:
Experimental or treatment group – this is the group that receives the experimental treatment, manipulation, or is different from the control group on the variable under study.
Control group – this group is used to produce comparisons. The treatment of interest is deliberately withheld or manipulated to provide a baseline performance with which to compare the experimental or treatment group’s performance.
Independent variable – this is the variable that the experimenter manipulates in a study. It can be any aspect of the environment that is empirically investigated for the purpose of examining its influence on the dependent variable.
Dependent variable – the variable that is measured in a study. The experimenter does not control this variable.
Random assignment – in a study, each subject has an equal probability of being selected for either the treatment or control group. You can use sampling techniques such as opportunity sampling or stratified sampling from a larger target population, but once subjects are chosen they must be randomly assigned to treatment and subject groups. If you are unsure what this means, let me know.
Double blind – neither the subject nor the experimenter knows whether the subject is in the treatment of the control condition.
Now that we have these terms defined, we can examine further the structure of the true experiment. First, every experiment must have at least two groups: an experimental and a control group. Each group will receive a level of the independent variable. The dependent variable will be measured to determine if the independent variable has an effect. As stated previously, the control group will provide us with a baseline for comparison. All subjects should be randomly assigned to groups, be tested simultaneously as possible, and the experiment should be conducted double-blind.
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