They answered a comparable number of questions correctly before the intervention ( 6.8 0.2 vs. 6.7 0.2 ) but differed significantly on this measure at six months ( 9.9 0.2 vs. 7.6 0.2 , mean difference 2.3 questions , 95 % confidence interval [ CI ] 1.5-3 .1 , p < 0.001 ) .