SFP - The Experimental Method Lesson

Learning Targets:

  • Identify independent, dependent, confounding, and control variables in experimental designs. 
  • Describe how research design drives the reasonable conclusion that can be drawn.
  • Distinguish between the random assignment of participants to conditions in experiments and random selection of participants, primarily in correlational studies and surveys.

AP psychology course and exam description, effective fall 2020. (n.d.). https://apcentral.collegeboard.org/media/pdf/ap-psychology-course-and-exam-description.pdf

The Experimental Method

(IV) is what you are manipulating within the experiment; (DV) is the change in behavior that occurs as a result of the IV.The experimental method is the only research method that can show cause and effect. It does so by manipulating variables to produce changes in outcome. The variables are called independent and dependent.

The independent variable (IV) is what you are manipulating within the experiment, usually what is added or taken away from the experimental group. The dependent variable (DV) is the change in behavior that occurs because of the IV. If you are conducting a study that involves the effects of drugs, your drug will be the IV, and the change in behavior because of the drug is the DV.

In an experiment, there are various groups. The group that is exposed to the IV is the experimental group. The group not exposed to the IV is the control group. The control group should be treated the same way as the experimental group with the only difference being a lack of exposure to the IV. This allows for the comparison of results and helps us to determine if the IV really caused a change in behavior.

When conducting an experiment, it is important to randomly assign participants to either the control or experimental group. Each participant should have a 50/50% chance of being chosen to participate in one of the groups. Sometimes events or factors that are out of our control can affect the DV. These are called confounding or extraneous variables.

Researchers must take account of confounding variables as they can alter the outcome of their study. The placebo effect (Placebo effect describes a change in behavior due to a fake treatment. For example, in a drug study, the control group would be given a placebo or sugar pill. A change in the participant's behavior after taking the pill would be an example of the placebo effect.) is an example of a confounding variable. Experimenter bias can also occur. This is when the experimenter unconsciously sways the outcome of the experiment or control group by their actions. Using a double-blind procedure will reduce experimenter bias.

Take a moment to read the scenarios below and determine the IV and DV for each experiment. Remember the IV is usually something that is being added or taken away and the DV is the effect.

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