Table 2.

Cochrane collaboration's tool for assessing risk of bias in the comparison of vitamin C versus placebo.

Studies	Random sequence generation	Allocation concealment	Blinding of participants and personnel	Blinding of outcome assessment	Incomplete outcome data	Selective reporting	Other bias
Anderson [30] 1972	low risk	low risk	low risk	low risk	low risk	low risk	unclear
Anderson [31] 1975	low risk	low risk	low risk	low risk	low risk	low risk	unclear
Audera [32] 2001	low risk	low risk	low risk	low risk	low risk	low risk	unclear
Elwood [33] 1977	unclear	low risk	low risk	low risk	low risk	low risk	unclear
Tyrrell [34] 1977	unclear	low risk	low risk	low risk	low risk	low risk	unclear
Lewib [35] 1975	unclear	unclear	low risk	unclear	low risk	low risk	unclear
Karlowski [36] 1975	low risk	unclear	low risk	low risk	low risk	low risk	unclear
Cowan [37] 1950	unclear	unclear	unclear	unclear	low risk	low risk	unclear