The Pearson coefficient measures the strength of linear correlations between two variables, but it is possible for two variables to have a nonlinear correlation as well.

Correlation shows the strength of a relationship between two variables and is expressed numerically by the correlation coefficient. The correlation coefficient's values range between -1.0 and 1.0.

Journal of the Royal Statistical Society. Series D (The Statistician), Vol. 39, No. 4 (1990), pp. 455-460 (6 pages) In this paper the robustness of some well known correlation coefficients, namely, ...

The Pearson correlation coefficient and the Spearman rank correlation coefficient are also appropriate for ordinal variables. The Pearson correlation describes the strength of the linear association ...

Craig Huhn, Correlation Revelation: The Search for Meaning in Pearson's Coefficient, The Mathematics Teacher, Vol. 110, No. 2 (September 2016), pp. 98-103 ...