TABLE 5-3 Mean Absolute Percentage Error (MAPE) of April 1, 2000, County Population Estimates (Official Series) Compared with April 1, 2000, Census Counts by County Population in 2000

County Population in 2000

Number of Counties

MAPE

All Counties

3,141

3.4

Under 2,500

115

6.9

2,500–4,999

177

4.3

5,000–9,999

405

3.7

10,000–19,999

651

3.3

20,000–49,999

879

3.2

50,000–99,999

390

2.6

100,000 and over

524

2.9

NOTE: The percentage error is calculated for each county as: (the 2000 census population count – the April 1, 2000, postcensal population estimate)/the 2000 census population count. The signs of these errors are dropped, and then the absolute errors are averaged across counties.

SOURCE: Blumerman and Simon (2006:Table 4).

county level. However, the ACS population controls are applied within subgroups defined by sex, age in 13 groups (0–4, 5–14, 15–17, 18–19, 20–24, 25–29, 30–34, 35–44, 45–49, 50–54, 55–64, 65–74, 75 and over), and race/ethnicity in 6 groups at the estimation area level. In practice the numerous cells in the sex by age by race/ethnicity cross-classification often have to be reduced by collapsing cells. A complex set of collapsing rules is employed, starting with collapsing categories of race/ethnicity to create collapsed cells with a minimum sample size of 10 persons and for which the weighting adjustment is less than 3.5. Subsequent collapsing of the sex by age cross-classification within collapsed race/ethnicity cells is then undertaken as necessary (U.S. Census Bureau, 2006:11-7).

The panel undertook a simple analysis in order to derive a rough indication of the level of error in the population controls being used in the ACS. For this purpose we dropped the race classification because of the problems with the differences in that classification between the population estimates and the 2000 census, retaining only Hispanic versus non-Hispanic (equivalent to collapsing the first five of the six race/ethnicity categories listed above). We also collapsed the 15–17 and 18–19 age groups into a single 15–19-year-old group. We then compared the sex by age by ethnicity cross-tabulations produced from the population estimates for 1999 with the corresponding cross-tabulations from the 2000 census for each of 1,950 estimation areas (excluding one estimation area used in the 2005 ACS that was a new county formed in 2001). The 1999 estimates were used because 2000 estimates were not published.



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