Projected Cancer Incidence for the State of Illinois and Illinois Counties

(revised July 2003)

Introduction

Projections of future cancer incidence in Illinois are calculated annually when incidence data are updated. For the state, cancer incidence is projected for all sites combined and selected sites for males and females of all races. For each of Illinois' 102 counties, cancer incidence projections are estimated for all sites combined, colon and rectum, and lung and bronchus for all races, both sexes and for female breast (invasive), cervix (invasive) and prostate among all races. This report presents cancer incidence projections for 2001, 2002, 2003 and 2004 at the state level. County cancer incidence estimates were calculated for the five-year time periods including 1997-2001, 1998-2002, 1999-2003 and 2000-2004 as well as the average annual incidence count for each respective five-year time period.

Methods

The age-specific rate method, an approach used to assess registry completeness, is employed to project cancer incidence in Illinois.¹ The method involves the multiplication of the most recent age-sex-race-specific cancer incidence rates for a group by the age-sex-race specific population estimates for that group. Projections at both the state level and the county level are only estimated for all races.

Revisions of cancer incidence projections will vary due to the dynamic nature of the registry database. Population estimates are updated regularly and will influence cancer incidence projections from year to year. Therefore, the use of these estimates to track year-to-year changes in cancer incidence is discouraged because the numbers may vary considerably, particularly for less common cancers and for small counties. For the purpose of tracking incidence changes, actual cancer incidence data should be used.

State Projections. The most recent Illinois cancer incidence data is reported for year 2000.² Age-specific, 2000 cancer incidence rates for each sex were calculated for the standard 18 five-year age groups. Population estimates by individual year for the same age-sex-race groups were available for Illinois only from 1990 through 2000. Therefore, it was necessary to compute population estimates for years 2001, 2002, 2003 and 2004. These estimates were obtained through linear extrapolation of the 1990-2000 population data for each respective age-sex-race-specific group using the growth rate regression model. An example is shown below for the population of females ages 50-54 in Illinois 1990 to 2004.

Expected incidence was calculated for 2001 by multiplying the age-sex-all races-specific cancer incidence rate for 2000 by the 2001 population for that subgroup and then summing expected incidence for all 18 age-sex subgroups to arrive at a total expected cancer incidence estimate for males and females in 2001 as shown in the following table.

County Projections. A modification of the procedures employed to determine state projections was used to project cancer incidence from all sites combined and selected sites for each of Illinois'102 counties. At the county level, it is necessary to aggregate data collected for five-year periods in order to protect confidentiality and produce more stable, interpretable data that may be viewed with reasonable confidence. Therefore, cancer incidence data for the five-year time period 1996-2000 served as a basis for calculating county-level projections.

First, age-specific cancer incidence rates for all races, both sexes were calculated for the 18 age groups. Expected cancer incidence was then calculated by multiplying the age-sex-specific cancer incidence rate for 1996-2000 by the 1997-2001 population estimate for that age-sex specific group and then summing expected incidence for all age groups to arrive at a total expected cancer incidence estimate for the 1997-2001 time period. The following example is shown for calculation of all sites combined cancer incidence expected in Sangamon County from 1997 through 2001.

This procedure was applied using county-level cancer incidence data among all races for cancers from all sites combined, colon and rectum, and lung and bronchus for both sexes, and female breast (invasive), cervix (invasive) and prostate.

Next, projected cancer incidence for those respective sites was calculated for the five-year periods, 1998-2002, 1999-2003 and 2000-2004 by applying the 18 age-specific rates for 1996-2000 to population estimates for the appropriate gender category for those time periods. Like the state projection methodology, it was necessary to extrapolate county population estimates for 2001, 2002, 2003 and 2004 to produce estimates for those time periods.

Linear Extrapolation of County Population Estimates. The county population estimates for years 2001, 2002, 2003 and 2004 were calculated from linear extrapolation of population data for 1990 through 2000 for each Illinois county using the same method applied to the state as previously described for females, ages 50-54 years.

Then, the population data for 1997, 1998, 1999 and 2000 and the extrapolated population estimates for 2001, 2002, 2003 and 2004 were aggregated to produce five-year population estimate totals for each of the age-sex-specific groups. The age-specific cancer incidence rates for 1996-2000 were applied in the same manner to project cancer incidence from all sites combined and selected sites for 1997-2001, 1998-2002, 1999-2003 and 2000-2004.

State Projections. The state-level projected cancer incidence for all sites combined and selected sites for 2001, 2002, 2003 and 2004 are presented in Table 1. Projections have been rounded to the nearest 10 cases.

County Projections. For each Illinois county, Tables 2, 3, 4, 5, 6 and 7 display projected cancer incidence for all sites combined, colon and rectum, lung and bronchus, and female breast (invasive), cervix (invasive) and prostate, respectively. Projected cancer incidence is presented for the five-year time periods 1997-2001, 1998-2002, 1999-2003 and 2000-2004. In addition, an average annual incidence projection also is presented for each time period. Projections have been rounded to the nearest 5 cases.

References

• NAACCR (North American Association of Central Cancer Registries). Standards for Completeness, Quality, Analysis, and Management of Data. North American Association of Central Cancer Registries, September 2000 (Standards for Cancer Registries; Vol. 3.). p. 26.



• Dolecek TA, Shen T, Snodgrass JL. Illinois Cancer Statistics Review, 1986-2000. Epidemiologic Report Series 03:5. Springfield, Ill.: Illinois Department of Public Health, July 2003.