New Resources: The Power of Microdata

By Trevor V. Mattos, MPP Candidate, Graduate Research Assistant, Public Policy Center at the University of Massachusetts Dartmouth

Recently, the Public Policy Center tapped into the American Community Survey Public Use Microdata Samples (PUMS) for two ongoing projects: [1] Socioeconomic Conditions for Immigrants in Worcester, [2] Pay Equity for Women in SouthCoast, MA. These new, extensive datasets allow us to measure a wide range of factors that affect outcomes for women and immigrants in communities around Massachusetts.

Since 2005, the American Community Survey (ACS) has collected detailed socioeconomic data from 250,000 individuals per month, or 3,000,000 people per year. The ACS now serves in place of the since-retired decennial census long form survey, dramatically improving accessibility to current data.  The U.S. Census Bureau provides ACS data to the public in two ways. First, ACS data is published on in pre-tabulated formats, which users can access via American FactFinder. Second, a subset of microdata files (roughly two thirds) for both households and individuals are made available for download and independent data analysis.

Microdata allows researchers at the Public Policy Center to answer highly specific, relevant questions about social and economic conditions in many different settings. Microdata are separated into state-level files, within which geographic areas containing roughly 100,000 people, called Public Use Microdata Areas (PUMA), further delineate the data. Careful use of PUMS’ complex survey data can yield nearly endless options for statistical inference and estimation. Using PUMS can be tricky though, as one first has to isolate the data of interest using less-than-intuitive geographical area codes, then weight the data appropriately. Finally, researchers must navigate statistical software like SPSS or Stata to derive estimates, margins of error, and statistics. A few examples of the analytic potential of such data follow:

[1] The median annual income, in 2013 U.S. dollars, for white, employed women over the age of 16, with a high school education (or less) in SouthCoast, MA is $23,880.27, while that of Hispanic or Latino women with matching characteristics is $16,398.19.


[2] In Worcester county central, or Worcester city proper, there are 17,943 native born individuals holding a 4-year university degree, while for the foreign-born population there are 6,401. However, comparing these estimates to total population estimates reveals that 16% of the foreign-born population holds a degree, while only 13% of native-born individuals in Worcester are 4-year degree-holders.


[3] For the average foreign-born worker in Massachusetts, a statistically significant relationship exists between ‘years in country’ and ‘average annual income’. Regression analysis of ACS microdata shows that for each additional year in country, the average foreign-born Massachusetts worker earns an additional $927.11 per year, in 2013 US$.


The Public Policy Center is surging ahead with a number of different projects supported by the new analytic potential of ACS Public Use Microdata Samples. We are excited to use these new tools to inform the conversation on social and economic issues that impact SouthCoast, Massachusetts and beyond!