Sandbox
Census errors
Can you trust Census data?
Freakonomics blog, New York Times, 2 February 2010
Justin Wolfers
Census Bureau obscured personal data—Too well, some say
Numbers Guy blog, Wall Street Journal, 6 February 2010
Carl Bialik
These stories describe problems with the Census Bureau' IPUMS (Integrated Public Use Mircodata Series) data, which provides subsamples of Census data to outside researchers. In order to protect the privacy of citizens, the records are altered slightly. For example, incomes may be rounded and ages may be tweaked by a small amount. Ideally this would make it impossible to identify any particular individual, while at the same time not introducing any important distortion into the overall demographic profile.
Unfortunately, it appears that serious distortions have resulted. A recent NBER working paper details the problems, which seem to be especially pronounced in data for ages 65 and greatedr The Freakonomics post reproduces the following graph from the paper
showing how total population estimates based on the microdata diverge from the actual Census counts for older Americans. Breakdowns within particular age groups are also distorted. For example, The Wall Street Journal article has an interactive graphic, illustrating how data released in 2006 showed year-to-year fluctuations from one age year to the next in the percentage of women who were reportedly married (those errors were corrected in 2007).
Submitted by Bill Peterson