Study	Reason for exclusion
Davis 2000	Neurodevelopmental abnormalities were compared between patients who received superoxide dismutase and those who received placebo. This was done by combining patients who received superoxide dismutase in two different studies and by combining patients in the placebo groups from those studies. One of the two studies had random allocation of patients to treatment / placebo and the other had non‐random allocation of treatment and placebo (groups were studied sequentially).
Rosenfeld 1996	Non‐random allocation of treatment and placebo (groups studied sequentially).