Predictors of inadequate bowel preparation in older patients undergoing colonoscopy: a systematic review and meta-analysis by Zhang, Yuanyuan, Wang, Lining, Wu, Wenbi, Zhang, Shi, Zhang, Min, She, Wenjing, Cheng, Qianqian, Chen, Nana, Fan, Pengxia, Du, Yuxin, Song, Haiyan, Hu, Xianyu, Zhang, Jiajie, Ding, Caiyan