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Andrew Mercer

Senior Research Methodologist

Andrew Merceris a senior research methodologist at Pew Research Center. He is an expert on nonprobability survey methods, survey nonresponse and statistical analysis, and his research focuses on methods of identifying and correcting bias in survey samples, as well as on the use of machine learning for survey data. He leads the Center’s research on nonprobability samples and co-authored several reports and publications on the subject. He has also authored blog posts and analyses making methodological concepts such as margin of error and oversampling accessible to a general audience. Prior to joining the Center, Mercer was a senior survey methodologist at Westat. He received a bachelor’s degree in political science from Carleton College and master’s and doctoral degrees in survey methodology from the University of Maryland. His research has been published in Public Opinion Quarterly and the Journal of Survey Statistics and Methodology.



MethodsOctober 9, 2018

Comparing Survey Sampling Strategies: Random-Digit Dial vs. Voter Files

A new telephone survey experiment finds that an opinion poll drawn from a commercial voter file produces results similar to those from a sample based on random-digit dialing.

February 8, 2017

A closer look at police officers who have fired their weapon on duty

About a quarter of all officers say they have ever fired their service weapon while on the job. Are some more likely than others to have fired their weapon in the line of duty?

Fact TankNovember 9, 2016

Why 2016 election polls missed their mark

There is a great deal of speculation but no clear answers as to the cause of the disconnect, but there is one point of agreement: Across the board, polls underestimated Trump’s level of support.

Fact TankOctober 25, 2016

Oversampling is used to study small groups, not bias poll results

As oversampling and its possible effect on presidential polls are spotlighted ahead of Election Day, learn more about this practice and how pollsters adjust for it.

Fact TankSeptember 8, 2016

5 key things to know about the margin of error in election polls

Some of the better-known statistical rules of thumb that a smart consumer might think apply in polls are more nuanced than they seem. In other words, as is so often the case in life, it’s complicated.

MethodsMay 2, 2016

Evaluating Online Nonprobability Surveys

Online nonprobability surveys are fast, cheap, and increasingly popular. We compared nine samples and found that accuracy varied substantially.