Colm’s areas of expertise include design of survey samples, questionnaire design and analysis, response and nonresponse error, and data quality. At NORC, his work centers on the development of methodological innovations in sample design and comparisons of data collection modes.

Colm has played a major role in such pivotal projects as the National Social Life Health and Aging Project (NSHAP), the National Children's Study (NCS), and the General Social Survey (GSS), along with his innovative work building NORC's national sampling frame using the U.S. Postal Service list of addresses. Most recently, Colm has acted as Principal Investigator on Sampling Strategies and Measure Development for the LGBT Aging Project (SAMLAP), leading the design of a two-phase address-based sample of LGBT older adults in the United States.

A faculty member in the Department of Statistics at the London School of Economics and Political Science from 1971 to 1998, Colm was the founding director of the school’s Methodology Institute. From 2009 to 2014, he served as the dean at the University of Chicago Harris School of Public Policy, where he has been a professor since 1998. He has acted as a consultant to numerous national and international organizations, including the United Nations, OECD, the International Association for Educational Assessment, and others. Colm formerly served as president of the International Association of Survey Statisticians.