Psychology
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