Recent efforts to make migration statistics comparable were mainly concerned with harmonising both the definition of migration related variables and the collection of data. The possibilities and limitations of these approaches are dealed with in the selected materials. You've an option to gather materials for your dissertation discussion chapter (or any other similar project) beforehead, and prepare a draft that later will be edited.
John Parker: "International Migration Data Collection" A paper prepared for the Policy Analysis and Research of the Global Commission on International Migration.
This paper discusses the modes of collecting migration data across a wide range of both sending and receiving countries. Using a questionnaire survey the paper discusses some terminological issues in migration statistics and also tries to assess the facility with which such data is collected, retrieved and analysed. The paper is available here: http://www.gcim.org/attachements/TP11.pdf
European Commission, Statistical Migration Data Migration and Asylum flows: collecting and analysing statistics
The United Nations Recommendations on Statistics of International Migration
The UN recommendations on statistics of international migration provide a framework for improving the quality and the comparability of international migration statistics. It also discusses facilitating the access of users to meaningful and sound information on key aspects of international migration. The recommendations are accessible here: http://unstats.un.org/unsd/pubs/gesgrid.asp?ID=116
Michel Poulain and Nicolas Perrin: "Can UN Migration Recommendations Be Met in Europe?" Article from Migration Information Source
The article discusses the how UN recommendations help improving international migration statistics in Europe.
J. Costanzo, C. Davis, and N. Malone: "Guide to International Migration Statistics: The Sources, Collection, and Processing of Foreign-Born Population Data at the US Census Bureau" (Population Division Working Paper #68, US Census Bureau, 2002)
The report reviews the methodological issues related to migration data collected in the U.S. by the Census Bureau. It discusses survey methodologies, the international migration-related items covered by the surveys, and the post-collection processing of the data.