Smoothed July 1, 1999 County Population Estimates


County population counts for April 2000 from the 2000 Census were released by the Census Bureau in March of 2001. Smoothed estimates of the population of North Carolina Counties for July 1, 1999 were released in May of 2001 by the State Demographer. These estimates were based upon a process of smoothing the estimates released in December of 2000 to more nearly match the trendline between the values for April 1, 1990 and April 1, 2000 from the 1990 and 2000 Censuses. This smoothing process was redone in early 2008 to account for 2000 Census corrections received between May of 2001 and November of 2007. The resulting new estimates were released by the State Demographer in April of 2008.

In August of 2000, certified population estimates for North Carolina and its counties as of July 1, 1999 were released by the Office of State Budget, Planning, & Management. In making these estimates, provisional MEDICARE enrollee values for July 1, 1999 were used. These values were not counts. They were estimates computed by assuming that the change, for each county, in numbers of MEDICARE enrollees from July 1, 1998 to July 1, 1999 was the same as the corresponding change in numbers of enrollees between July 1, 1997 and July 1, 1998.

In September of 2000, actual July 1, 1999 MEDICARE enrollee counts, for each county in North Carolina, were received by this office. These values were used to make revised population estimates for North Carolina and its counties as of July 1, 1999. These revised estimates were released in December of 2000. For the estimates released in December of 2000, the county boundaries are those in effect for the 1990 federal census, except for minor adjustments for twenty-seven counties. The state estimate was produced by adjusting the 1999 state estimate for North Carolina released in December of 1999 by the United States Bureau of the Census in cooperation with this office, the FSCPE(Federal State Cooperative Program for Population Estimates) estimate, for corrections to major institutional populations for April 1, 1990 and July 1, 1999 and for the difference between actual and estimated state MEDICARE totals for 1999. The county estimates are averages of two sets of estimates, a set of modified Census Bureau estimates, and a set of Ratio/Correlation estimates produced by this office.

Modified Census Bureau Estimates

In March of 2000, the Population Division of the United States Bureau of the Census released their 1991 through 1999 state and county population estimates for North Carolina. They used an administrative records technique similar to the 1980's technique of the same name. These estimates used new, slightly adjusted, April 1, 1990 population totals, based on revised county boundaries for twenty-seven North Carolina counties. In making their 1999 estimates, the Census Bureau assumed that the 1999 institutional population of each county would be the same as for 1998. By May of 2000, we were able to obtain the 1999 data for all of our military bases and for the vast majority of the other institutions whose data were directly used in making their 1999 estimates for our counties. As a result, we adjusted their 1999 county and state estimates for the differences between their 1999 institutional populations and this new data, as well as for some corrections to their institutional data for April 1990. In December of 2000, we adjusted their estimates for changes between the actual and estimated county and state MEDICARE totals for 1999.

Ratio/Correlation Estimates

Two basic procedures were used to build these estimates. First, we used changes in the numbers of MEDICARE enrollees to estimate the population 65 years of age and older. MEDICARE enrollee counts for July 1, 1989 and July 1, 1990 were used to estimate values for April 1, 1990. Numbers of MEDICARE enrollees for April 1990 were subtracted from July 1, 1999 values and the resulting differences were assumed to approximate the changes in the numbers of persons aged 65 and older between April 1, 1990 and July 1, 1999. These changes were added to the new, revised April 1, 1990 population counts for persons 65 years of age and older to create the final estimates for this age group.

Second, we used a standard ratio/correlation method to estimate the population aged 0-64 for all counties except Pitt, which had a countywide special census in April of 1998. The data series used were automobile and truck registrations (X1), school enrollment in grades 1 through 8 (X2), and a three year sum of births (X3). For 1999, the three year sum of births was the sum of final calendar year values for 1997, 1998 and 1999; for 1990, the sum of values for 1988, 1989, and 1990. In order to remove the effects of United States military deployments in the Persian Gulf in late 1990 and early 1991, automobile and truck registration totals for the base point (January 1991) were estimated as the average of corresponding values for January 1990 and for January 1992. The prediction equation for each North Carolina county, excluding Pitt, is given by

y = -0.038424 + 0.455019 * X1 + 0.320879 * X2 + 0.248463 * X3,

where y represents the estimated ratio of percentage shares of nongroup quarters population and each of the series indicators (X1, X2, and X3) represents the ratio of percentage shares of the associated variable. The equation coefficients were derived by least squares regression, using series indicator and population values for 1980 and 1990. The results of this equation were adjusted for the extra 1/4 year of the estimate period by linearly expanding the change in y from the assumed 1990 value of 1.0. The nongroup quarters 0-64 population estimates derived from this equation were combined with independent estimates of the population of military barracks, college dormitories, and other institutions to yield estimates of the total 0-64 population.

Finally, we added a value for Pitt County for the 0-64 population for July 1, 1999 based on the April 1998 special census. The July 1, 1998 to July 1, 1999 growth in the 0-64 population for Pitt County was assumed to be the same as that indicated by the data series mentioned above in the absence of any special census.

The state estimate for 1999 was the adjusted one mentioned above. Subtraction of the sum of the county populations 65 and older from this estimate produced a control for the 0-64 population estimates. There was no state control for the population 65 and older.

Methodology --- Age, Race, and Sex Detail

To calculate the populations for the different age, race, and sex groups, I used a relatively simple process. First, April 1, 1990 and April 1, 2000 Census counts for each county by 384 age, race, and sex cells (96 age values: 0,1,2,...,94, and 95+; white/other; male/female) were interpolated (age cohort interpolation for non-institutional populations; age group interpolation for institutional populations) to July 1, 1999. (In early 2007 and again in early 2008, this process was revised.) Next, the 384 cells for each county were proportionately adjusted to sum to the county total population. Finally, the appropriate age cells were summed to form each group.

Last Update: April 9, 2008