Researchers may choose a correlational study when an experiment isn't realistic, such as controlling how much people exercise for weeks.
In a correlational study, researchers don't manipulate variables; they measure what participants already do or feel and look for a relationship.
Correlational studies can't prove cause and effect because of the directionality problem and the third variable problem.
The directionality problem means we can't tell which variable affects which — exercise might improve mood, or good moods might lead to more exercise.
The third variable problem means another variable, like physical health, could explain both measured variables; in experiments, random assignment helps control this.
A correlation shows two variables are related but cannot establish causation; that requires an experiment.
Correlational studies still need a testable hypothesis, clear operational definitions, and careful sampling.
Key terms
correlational study
A study that measures existing variables, without manipulating them, to look for a relationship between them.
directionality problem
In a correlation, not knowing whether variable A affects variable B or B affects A.
third variable problem
The possibility that another, unmeasured variable is responsible for the relationship between two measured variables.