Multivariate logistic regression analysis revealed that , after adjusting for gender , body mass index , abdominal compression , position change , insertion time to cecum , and length of scope at cecum , only WE was significantly associated with painless insertion compared with AI ( odds ratio ( OR ) = 0.08 , 95 % confidence interval ( CI ) = 0.03-0 .24 , P < 0.001 ) or WI ( OR = 0.14 , 95 % CI = 0.05-0 .40 , P < 0.001 ) .