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Table 5 Elements of implementation for causal mediation analysis

From: Implementation and reporting of causal mediation analysis in 2015: a systematic review in epidemiological studies

References Sample sizea Power and sample size calculation for mediation analysis Exposure-mediator interaction in the model Power and sample size calculation for interaction analysis Lack of power mentioned as a non-causal explanation of findings
Studies with negative findings
 Freeman et al. [28] N = 51 for adjusted and n = 54 for unadjusted analysis 80 % power to detect large indirect effects (Fritz M, Mackinnon DP. Required sample size to detect the mediated effect) Not reported Not applicable Limited power to detect whether mediated effects were statistically significant
 Jackson et al. [29] N = 26,197 Not reported No No
 Kositsawat et al. [30] N = 1765 Not reported Not reported Not applicable No
 Louwies et al. [31] N = 55 Not reported Not reported Not applicable Called for cautious interpretation given small sample size
 Mendola et al. [33] Varied by outcomes (i.e. 1 study site did not report infant apnea) Not reported No No
Studies with positive findings
 Banack et al. [26] N = 7212 Not reported No No
 D’Amelio et al. [27] N = 37 80 % power, two-sided significance level of 0.05, to detect differences in uOC greater than 1.71 (t test on log-scale) No Acknowledged small sample size as a limitation
 Lu et al. [32] N = 58,322 for metabolic
N = 19,572 for fibrinogen
Not reported No No
 Messerlian et al. [34] All singleton births (n = 18,147); only first births (n = 8651) Not reported Not reported Not applicable Limited power mentioned; limited sample size to evaluate spontaneous and induced preterm birth separately
 Raghavan et al. [35] Varied by mediators (n = 2159 for diet score; and n = 2098 for physical activity index) Not reported Not reported Not applicable Lack of power to examine the association in the mediation framework
 Rao et al. [36] N = 433 Not reported X No No
 Song et al. [37] Varied by mediators (biomarkers) Not reported No Despite some significant mediation by several biomarkers, the sample size may still not be large enough to provide more precise estimates or to detect mediation by other potential factors with smaller mediation effects
 Xie et al. [38] N = 167 Not reported X No Small sample size acknowledged
  1. aSmallest sample size used in the causal mediation analysis