The Census Bureau today released five sets of population estimates for the nation as of April 1–but not from the soon-to-be-released 2010 Census count. The estimates are based on an alternative measurement technique, called demographic analysis, that agency officials say employs plausible assumptions about population change. The demographic analysis estimates range from a low of 305.7 million to a high of 312.7 million. The first numbers from the 2010 Census, which will include a national population total and state totals for reapportionment purposes, will be released later this month.

At a news conference today, Census Bureau Director Robert Groves said the five different estimates all make “plausible assumptions.” The analysis will be among three major tools used by the bureau to evaluate the quality of the 2010 Census. The other two include quality measures such as mail return rates from the census itself, and a post-census quality-check survey for which results will be released in 2012.

The demographic analysis methodology is based mainly on use of birth, death, immigration and Medicare records since the 2000 Census. For the population under age 65, bureau officials subtracted the number of deaths from the number of births, added in immigration and subtracted emigration. For the population ages 65 and older, the analysis relied mainly on Medicare enrollment data, supplemented by estimates from the Current Population Survey of older Americans not enrolled in Medicare.

The data exercise sounds deceptively simple, but as this technical paper demonstrates, Census Bureau experts had to make numerous choices based on sometimes-incomplete information. The release of five different sets of estimates reflects a lack of certainty about the data on which the estimates were based. Each of the five sets is based on a different estimate of net international migration over the past decade. The lowest and highest estimates also are based on different estimates of births, deaths and the 65-and-older population. The range of the estimates is 7 million people, of which 5 million is due to differing net immigration estimates, especially counts of unauthorized immigrants.

Bureau officials have used this alternative technique for decades to check the quality of the door-to-door census count, and to improve the accuracy of the annual population estimates between census counts.  A decade ago, the bureau’s initial total derived by demographic analysis was markedly lower than its 2000 Census count–279.6 million, compared with 281.4 million. A major reason was that demographic analysis had underestimated unauthorized immigration; there also were issues with birth statistics and race classification. For 2010, bureau officials attempted to improve their immigration estimates by analyzing data from the American Community Survey, which went fully operational in mid-decade, and by consulting outside experts.

In addition to the national population totals, the five series of estimates also include numbers for men and women, for each single year of age, for race groups (only black and non-black because of data limitations), and for the Hispanic population under age 20 (again, because of data limitations, the full Hispanic population was not estimated). There are no estimates for states or other geographic units  below the national level, again because of limited data.

Although the estimates released today are not 2010 Census numbers, bureau officials will use them to help evaluate the quality of the census count. In particular, after detailed race, age and gender numbers from the census come out in 2011, demographers will examine any patterns of difference between the census counts and demographic analysis estimates to see how both measurements can be improved.

At a news conference, Groves emphasized that the estimates had been developed independently of the 2010 Census counts; the demographic analysis team was “sequestered,” he said, from the work on 2010 Census totals. The demographic analysis released today also was not based on the annual population estimates that use a similar methodology; the last national estimate said that as of July 2009, the U.S. population was 307 million.