Measure of how one variable changes with another, for example, chart scoring ability and years of experience are positively correlated. Measures of correlation range from -1.00 (indicating a perfect negative correlation—as variable x increases, variable y decreases) to +1.00 (indicating a perfect positive relationship—as variable x increases, variable y increases). A correlation equal to 0.00 means that two variables are not linearly related. One should not infer cause from correlation; two variables can be correlated without one causing the other. For example, in most cities the number of churches and the number of criminals are positively correlated, but one does not cause the other. Both are correlated to a third factor, population.