In a separate analysis , subjects more likely to drop-out were those with a lower educational level [ odds ratio ( OR ) = 3.26 , 95 % confidence interval ( CI ) = 1.22-8 .70 , P = 0.018 ] and a higher level of obesity ( OR = 0.974 , 95 % CI = 0.95-0 .99 , P = 0.010 ) .