Topics: Experiment, Psychology, Scientific method Pages: 5 (1470 words) Published: February 6, 2014

Psychologists conduct three main types of research: experimental, correlational, and clinical. The experiment is an investigation seeking to understand relations of cause and effect. The experiment changes a variable, or a cause, and measures how it changes the other variable in the experiment (effect). Concurrently, the investigator of the experiment tries to hold all other variables constant so he/she can attribute any changes to the manipulation. The manipulated variable is called the independent variable. The dependent variable is what is measured. For example, an experiment designed to determine whether playing violent video games causes aggression to the players. Two groups of children are randomly selected to play a violent game, or a non-violent one for one hour. This would be considered the independent variable because it can be easily manipulated by the experimenter. Afterwards, a large may be placed in front of each child for one hour; while the experimenter records the number of times a child hits, kicks, punches, or shows aggression toward the doll. This would be considered the dependent variable since it is the variable that remains constant and is being measured. The group receiving or reacting to the independent variable is the experimental group; the control group does not receive the independent variable but should be kept identical in all other respects. Using two groups allows for comparison to be made and causation to be determined.

In order for researchers to draw conclusions about the result of the controlled experiment, it is important that certain other conditions are met as well. The researcher identifies a specific population to be studied. Because the population may be too large to study effectively, a representative sample of the population may be collected. The representativeness is the degree to which a sample reflects the diverse characteristics of the population that is being studied. Radom sampling is one way of ensuring maximum representativeness. Once the sampling has been done, the subjects are randomly assigned into both the experimental and control groups. Random assignment is done to assure that each group has minimal variances.

Sometimes researchers or subjects unknowingly influence the results. To avoid this from occurring, researchers use a single- or double- blind design experiment. Single- blind design means that the subject is not in knowledge of whether he/she is in the control or experimental group. In a double- blind design, neither the subjects nor the researcher know who are in the two groups. Double-blind studies are designed so that the experimenter does not inadvertently change the responses of the subjects. In a double blind design, a third party has the appropriate records so that the data can be analyzed later. In some double blind experiments, the control group is given a placebo, a seemingly therapeutic object or procedure that causes the control group to believe they are in the experimental group, but it actually contains none of the tested material.

Correlational research involves assessing the amount of association between two or more variables or characteristics of interest that occur naturally. Researchers do not directly manipulate variables, but rather observe naturally occurring differences. If the characteristics under consideration are related, then they are correlated. However, correlation does NOT prove causation; it only shows the strength of the relationship among variables. A researcher may note that poor school performance may be correlated with lack of sleep, but we don’t know if lack of sleep caused the poor performance, vice versa, or if some unidentified factor influenced both of them. If an unknown factor is playing a role, it is known as a confounding or third variable, problem. A way to gather information for correlational studies is through surveys. Using questionnaires or interviews, a researcher can collect a large amount of...
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