Ren, W., T. Krenzke, B. West, and D. Cantor. “An Evaluation of the Quality of Interviewer and Virtual Observations and Their Value for Nonresponse Bias Reduction”. Survey Research Methods, vol. 16, no. 1, Apr. 2022, pp. 97-131, doi:10.18148/srm/2022.v16i1.7767.