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Table 7 Summary statistics from main analyses based on the risk ratio (RR) and the risk difference (RD)

From: What are the relative risks of mortality and injury for fish during downstream passage at hydroelectric dams in temperate regions? A systematic review

AnalysisRelative risk ratio (RR)Absolute risk difference (RD)
(A) Global meta-analyses
 Fish injury (k = 104)3.17 (95% CI 1.74, 5.78); 217%0.093 (95% CI − 0.04, 0.22); 9.3%
 Immediate mortality (k = 162)3.35 (95% CI 2.38, 4.69); 235%0.122 (95% CI 0.05, 0.19); 12.2%
 Delayed mortality (k = 256)Could not obtain stable resultsCould not obtain stable results
(B) Effects of moderators
 Fish injury
  Turbines (k = 54)5.06 (95% CI 1.95, 13.08); 406%0.100 (95% CI − 0.04, 0.24); 10.0%
  General infrastructure (k = 21)3.50 (95% CI 1.09, 11.27); 250%0.184 (95% CI − 0.01, 0.38); 18.4%
  Bypasses (k = 4)0.18 (95% CI 0.05, 0.65); -82%− 0.099 (95% CI − 0.24, 0.04); − 9.9%
  Spillways (k = 4)8.92 (95% CI 1.56, 50.87); 792%0.199 (95% CI − 0.07, 0.46); 19.9%
 Immediate mortality
  Turbines (k = 136)3.83 (95% CI 2.74, 5.36); 283%0.134 (95% CI 0.06, 0.21); 13.4%
  General infrastructure (k = 4)4.71 (95% CI 1.85, 12.02); 371%0.074 (95% CI − 0.03, 0.18); 7.4%
  Bypasses (k = 8)1.11 (95% CI 0.53, 2.32); 11%0.056 (95% CI − 0.04, 0.15); 5.6%
  Sluice (k = 3)3.61 (95% CI 0.74, 17.54); 261%0.112 (95% CI 0.00, 0.22); 11.2%
  Spillways (k = 9)2.01 (95% CI 1.04, 3.89); 101%0.084 (95% CI − 0.00, 0.17); 8.4%
(C) Taxonomic analyses
 Fish injury
  Alosa (k = 6)2.27 (95% CI 1.42, 3.61); 127%0.126 (95% CI 0.03, 0.22); 12.6%
  Lepomis (k = 8)3.63 (95% CI 0.91, 14.46); 263%0.351 (95% CI − 0.28, 0.98); 35.1%
  Oncorhynchus (k = 66)4.23 (95% CI 1.81, 9.85); 323%0.048 (95% CI − 0.16, 0.25); 4.8%
 Immediate mortality
  Alosa (k = 12)2.44 (95% CI 1.07, 5.53); 144%0.094 (95% CI − 0.05, 0.24); 9.4%
  Oncorhynchus (k = 128)3.37 (95% CI 2.31, 4.91); 237%0.098 (95% CI 0.02, 0.18); 9.8%
 Delayed mortality
  Alosa (k = 9)2.41 (95% CI 0.74, 7.85); 141%0.097 (95% CI − 0.00, 0.20); 9.7%
  Anguilla (k = 5)13.75 (95% CI 6.87, 27.51); 1275%0.292 (95% CI − 0.25, 0.84); 29.2%
  Salmo (k = 5)5.69 (95% CI 0.64, 50.65); 469%0.329 (95% CI − 0.20, 0.86); 32.9%
  Oncorhynchus (k = 208)Could not obtain stable resultsCould not obtain stable results
  1. For RR, % increase risk was calculated as the percent relative effect (when RR > 1) = (RR − 1) × 100. For RD, % increase risk was calculated as the percent absolute effect = RD*100. Note, a decrease in the risk of fish injury/mortality from passage over/through hydroelectric infrastructure compared to control groups is indicated by a value of < 1 for RR and < 0 for RD. k: number of data sets (i.e., effect sizes); CI: 95% confidence intervals