在统计学里，「Phi相关系数」（英语：Phi coefficient）（符号表示为： 或 ）是测量两个二元变量（英语：binary variables or dichotomous variables）之间相关性的工具，由卡尔·皮尔森所发明 。他也发明了与Phi相关系数有密切关联的皮尔森卡方检定（英语：Pearson's chi-squared test。一般所称的卡方检定，若未明指种类，即指此），以及发明了测量两个连续变量之间相关程度的皮尔森积差相关系数（英语：Pearson's r。一般所称的相关系数，若未明指种类，即指此）。

In statistics, the phi coefficient (also referred to as the "mean square contingency coefficient" and denoted by φ (or r_φ)) is a measure of association for two binary variables. Introduced by Karl Pearson, this measure is similar to the Pearson correlation coefficient in its interpretation. In fact, a Pearson correlation coefficient estimated for two binary variables will return the phi coefficient. The square of the Phi coefficient is related to the chi-squared statistic for a 2×2 contingency table (see Pearson's chi-squared test)