Table 2: The Effect of Zinc Lozenges on the Duration of the Common Cold: Combining the P-Values of the Placebo-Controlled Trials

Trials Being Combined No. of Trials χ2 df P
All trials 13 154.0 26 10–19
Low Zn dose (<75 mg/day) 5 5.7 10 0.8
High Zn dose (>75 mg/day) 8 148.3 16 10–22
  Zn-acetate [21,22,25] 3 107.7 6 10–20
  not Zn-acetate [7,19,20,23,24] 5 40.6 10 10–5

The P-values of the individual trials are combined by using the Fisher method (see the Methods section). The combined χ2 value is calculated from the –2×ln(P) values on the right side of Table 1. The combined P-values are separately calculated for low dose and high dose trials. Finally, the high dose trials are divided to those which used zinc acetate and to those which used zinc salts other than acetate.