The Ever-changing Census

Let me start out by saying that the United States Census is THE go-to source for historical statistics on the U.S. population. Now let me enumerate the ways in which it drives me crazy.

  1. The Murphy’s Law of Statistics: Statistics will never be compiled exactly the way you want them. I learned this one early on as a reference librarian. If you want the data broken out by sex, you’ll only find it broken out by race.
  2. Census data is rarely comparable from one decade to another.
    • Boundaries change over time so that if you look at statistics from 1790 Louisville, Ky. and 1970 Louisville, Ky. you are looking at two very different cities in terms of what areas are counted. And then there’s Standard Metropolitan Statistical Areas (SMSAs), Consolidated Metropolitan Statistical Areas (CMSAs), and Primary Metropolitan Statistical Areas (PMSAs). The short version of this is that the Bureau of the Budget created a list in 1949 of standard metropolitan areas that constituted the core areas of population, economic activity and social interaction which are generally centered around a city. And like everything else about the census, these areas have changed over time (in 1958, 1971, 1975, 1980, 1990, and 2000).
    • Methods changed over time as to how the data was collected. A notable change for those of us studying people’s occupations is the change from counting “gainful workers” and members of the “labor force”. Until 1930 anyone who said they had an occupation was listed as being a “gainful worker” in that occupation. Starting with the 1940 census the rule changed. Only people who were employed or seeking work during the week the census was taken were counted as being in the labor force.
    • And if that weren’t enough to make you go cross-eyed, social standards changed over time as well. So tables from the 1920s give occupational data from 10 years of age and up, 1940s give it for 14 year olds and up, and 1970 gives it for 16 years and up.

All that being said, the Census is still the go-to source. Why? It’s a really rich source of information. So if you have a need for historical population or economic data, you’re probably going to need to deal with the census one way or another.

Some tips

  • While a lot of the census info is available online, Ekstrom Library also carries print versions in the Reference Collection under HA 201. While the online is great if you can’t get to the library, the print collection is sometimes easier to use because of the sheer size of each census and the number of tables it includes.
  • Write it down! Make sure you get all the info from the title indicating what the table includes (ex. “Detailed occupation of employed persons by sex, for the state, and for cities of 100,000 or more: 1940”) as well as the table and page numbers and citation info for that book or webpage.Try to be as clear as possible about exactly what the statistics represent so you don’t mis-state the facts later.
  • Give yourself plenty of time and don’t be afraid to browse. Sometimes you’ll discover some great information you never knew existed.


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