Standardized mean differences of trace element concentrations: hemodialysis participants versus healthy controls. The small solid gray diamonds represent the standardized mean difference (SMD) in trace element concentrations between hemodialysis patients and controls (for each individual study). The large red crosses represent the random-effects pooled SMDs. Results were pooled only for trace elements that were measured in at least three studies and for which the sign test was statistically significant. The shaded gray region denotes SMD representing differences between hemodialysis patients and controls, which are moderate or small (<0.8 standard deviation). Data points outside the gray region represent large differences between hemodialysis patients and controls (SMD ≥0.8 standard deviation).