CONTROL GROUPS AND PLACEBOS

Correlations

A systematic relationship between two or more variables. A correlation alone does not tell us anything about causation.

Experiment

Researcher systematically changes an independent variable, while holding all other variables constant, and observes the effects on a dependent variable. 

Independent Variable IV

Variable that the experimenter changes/ variable that you think might be causing the change in the DV. 

Dependent Variable DV

Variable that the experimenter measures. 

Some Factors that Influence the Validity of the Experiment

• Sampling Bias

• Self Selection Bias

• Confounding or Extraneous Variables

• Participant Expectations

• Experimenter Behavior and Expectations

Experimental Sample Groups

Participants in the experiment need to be representative of the larger group, failure to do this can result in selection/sampling bias. 

Random Assignment

Experiments rely on random assignment of participants to experimental groups, this helps to eliminate any self selection bias that might occur.

Control Groups

A group of participants who experience the same things as the other experimental group, except for the independent variable.

Placebo Effect

A positive response to a nonspecific or ineffective treatment, often caused by the recipient’s expectations or beliefs regarding the intervention. 

How Do We Control for Placebos

Blind Trials, participants do not know which experimental condition they are in ( a type of control group called placebo group ).

Some Factors That Influence the Validity of the Experiment (and how to reduce them)

• Sampling Bias, ensure the sample is representitive.

• Self Selection Bias, random assignment to experimental groups

• Confounding or Extraneous Variables, use control groups

• Participant Expectations, use placebo groups and blind testing when possible