 It is possible to combine the results of several small studies to produce evidence that is stronger than that available from each study alone — a statistical method known as meta @-@ analysis . One of four such analyses , conducted in 2006 , looked at 19 studies on a total of 1 @,@ 084 patients . It concluded that half the patients achieved a 50 % reduction in seizures and a third achieved a 90 % reduction . 
