When ISIS-4 is added to the preceding eight RCTs, the fixed effects model (driven heavily by the large sample size of ISIS-4) indicates no beneficial effect of magnesium (OR= 1.02 [0.96-1.09]) while the random effects model that takes into account the heterogeneity among these trials suggests that magnesium may reduce mortality (OR= 0.69[0.47-1.02]). Thus, the random effects model suggests that one must search for possible sources of differences between ISIS-4 and the preceding trials. Two important differences that appear to be acting in concert to bias ISIS 4 towards a null effect of magnesium include: