Unlike an experiment, where the researcher manipulates an independent variable and measures a dependent variable, a researcher using correlational methods identifies and measures co-variables.

Usually, psychologists calculate a correlation coefficient, which indicates how strongly the co-variables are linked to each other. -1 indicates a perfect negative correlation (as one variable increases, the other decreases) +1 indicates a perfect positive correlation (as one variable increases, the other also increases). Correlation coefficients can be between +1 and -1. A correlation coefficient of +0.8 would be considered a strong positive correlation, while a correlation coefficient of +0.2 would be considered to be a weak positive correlation.