Basarir H. Poor, multidimensionally speaking: evidence from South Africa. J Afr Econ. 2011 Jun 1;20(3):463-504. doi: 10.1093/jae/ejr001
Reed (Earnshaw) SJ, Reed JH. The use of statistical quality control charts in monitoring interviewers. Proceedings of the Survey Research Methods Section, American Statistical Association. 1997 Jan;893-8.