The paper describing the elicitation of the expert opinions about migration flows in Europe:
Wiśniowski A, Bijak J, Christiansen S, Forster JJ, Keilman N, Raymer J and
Smith PWF (2013) Utilising expert opinion to improve the measurement of international migration in Europe.
Journal of Official Statistics 29 (4), 583-607. Available at
http://dx.doi.org/10.2478/jos-2013-0041