<qa>  What is the name of the study that compared the clinical outcomes and costs of the walls14. Mehta S, Ozden ZS, Dhanireddy S, Pleskow DP, Chutanni R. Endoscopic single versus double bilateral Wallstents for palliation of malignant Bismuth type IIIIV hilar strictures: comparison of clinical outcomes and costs abstract. Gastrointest Endosc 1999;49:AB234. 