A positive correlation is a relationship in which two variables tend to increase or decrease together. As one rises, the other tends to rise; as one falls, the other tends to fall.

Height and weight, study time and exam scores, and years of education and income often show positive correlations. The strength of the association is expressed by a correlation coefficient ranging from 0 to +1.00. A coefficient near +1.00 indicates that the points on a scatterplot fall close to an upward-sloping line; a coefficient near 0 indicates little linear relationship.

Positive correlation does not establish causation. A third variable may drive both measures, or the causal direction may be ambiguous. Correlational research maps associations that can then be tested experimentally when manipulation is possible and ethical.

When two measures systematically move in the same direction, the relationship is a positive correlation.