The procedure for establishing mediation, i.e., determining that an independent variable X affects a dependent variable Y through some mediator M, has been under debate. The classic causal steps require that a "total effect" be significant, now also known as statistically acknowledged. It has been shown that the total-effect test can erroneously reject competitive mediation and is superfluous for establishing complementary mediation. Little is known about the last type, indirect-only mediation, aka "full" or "complete" mediation, in which the indirect (ab) path passes the statistical partition test while the direct-and-remainder (d) path fails. This study 1) provides proof that the total-effect test can erroneously reject indirect-only mediation, including both sub-types, assuming least square estimation (LSE) F-test or Sobel test; 2) provides a simulation to duplicate the mathematical proofs and extend the conclusion to LAD-Z test; 3) provides two real-data examples, one for each sub-type, to illustrate the mathematical conclusion; 4) in view of the mathematical findings, proposes to revisit concepts, theories, and techniques of mediation analysis and other causal dissection analyses, and showcase a more comprehensive alternative, process-and-product analysis (PAPA).

翻译：关于建立中介效应（即确定自变量X通过某个中介变量M影响因变量Y）的程序一直存在争议。经典的因果步骤法要求“总效应”显著，这现在也被称为统计认可。已有研究表明，总效应检验可能错误否定竞争中介效应，且对于建立互补中介效应是多余的。关于最后一种类型——仅间接中介效应（又称“完全”或“全”中介效应），即间接（ab）路径通过统计分区检验而直接剩余（d）路径未通过的情况，目前知之甚少。本研究：1）在假设最小二乘（LSE）F检验或Sobel检验的情况下，证明总效应检验可能错误否定仅间接中介效应，包括其两个子类型；2）提供模拟验证数学证明，并将结论扩展至LAD-Z检验；3）提供两个实际数据案例（每个子类型各一个）以说明数学结论；4）鉴于数学发现，提出重新审视中介分析及其他因果剖析分析的概念、理论和技术，并展示更全面的替代方案——过程与产品分析（PAPA）。