Whibley D, AlKandari N, Kristensen K, Barnish M, Rzewuska M, Druce KL, Tang NKY. Sleep and pain: a systematic review of studies of mediation. Clin JPain. 2019 Jun;35(6):544-58. doi: 10.1097/AJP.0000000000000697
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.