NEWS

Cancer Rates Change Slightly With Census Data Correction

James Schultz

In its latest annual update of the nation’s cancer rates, the National Cancer Institute’s Cancer Statistics Review includes incidence, mortality, and survival rates for all cancers for the period 1975–2000, using corrected population estimates from the U.S. Census Bureau. The bottom line, according to Brenda Edwards, Ph.D., associate director of NCI’s Surveillance Research Program, is that cancer rates on the whole seem to be in slight decline, even as incidence and mortality are on a modest upswing for certain groups.

"What are the patterns in cancer rates? You can’t answer that simplistically," Edwards said. "You have to compare like to like. Cancer is a function of age; its incidence is higher the older you get. The population is aging and growing at the same time. You have to take that into account."

The Cancer Statistics Review is produced annually by the NCI’s Surveillance, Epidemiology, and End Results (SEER) program. In general, cancer death rates were down slightly in the late 1990s. But looking over 25 years, Edwards pointed out, cancer death rates were increasing and then reached a plateau. For women in particular, the decline has leveled out and in recent years has stalled. "That’s an area of concern," she said. "We don’t know what’s happening exactly, or what’s driving it." On the surface, at least, a small increase in female cancer rates could be the result of a rise in lung cancers, but the evidence is not altogether conclusive, Edwards said.

The inclusion of the 2000 census data will not have a substantial effect on cancer rates. Some rates for less common cancers, cancers in minority populations, smaller geographic areas, or cancers among specific age groups may ultimately be affected, however. Updates to American Indian and Hispanic populations should result in slight increases in their cancer rates, but overall changes should remain relatively small—in the neighborhood of 1% to 2%.

Where cancer rates were most affected by the latest revision were in less populated, smaller, rural locales or in adjacent urban and suburban areas where there was substantial migration of residents. According to the NCI, any substantial change in the overall numbers could affect small-area rates by as much as 20%, unlike larger population concentrations. If a new census population estimate is larger than an earlier one and the number of cancer cases remains the same, incidence and mortality rates will be smaller. Similarly, rates will increase if overall population decreases.

An NCI fact sheet cited the concentration of African Americans in the Atlanta metropolitan area as an example of how population migration can affect cancer rates. Populations there were higher than previously estimated as a result of suburban migration not fully captured by the 1990 census. As a result of the underestimate, cancer rates were actually lower among Atlanta-metro blacks than originally calculated.

"This happens every time a census is done," said Jennifer Madans, associate director for science at the National Center for Health Statistics (NCHS). "There are always a lot of numbers out there. None of the data is perfect; remember that information is collected at different levels of geography and demographics. When you look at rates, you have to make sure you know what you’re looking at."

One inherent limitation is the pace of census-taking. Ten-year-old data can be used as a base, but must be refreshed as often as is practical. Every year, through an interagency agreement, the NCI receives updated Census Bureau data that includes information mined from Internal Revenue Service and Medicare records (release of confidential information is not permitted). Numbers are obtained state by state, county by county, and details are available on age, race, gender, and ethnicity. Births and deaths are also recorded. To determine rates of cancer incidence and mortality, NCI divides the number of cancer cases or deaths in a given geographic area by the total number of people in that area. But because many Americans move, and often, there remain uncertainties that must be compensated for, leading to a measure of statistical uncertainty.

"You have to be very cautious in interpreting cancer rates for specific racial and ethnic groups in a given county," said Barry Miller, Ph.D., an epidemiologist in the Cancer Statistics Branch of the National Cancer Institute’s Surveillance Research Program. "One of the shortcomings of the [IRS] records is that race isn’t estimated on tax forms. So you have to make some assumptions. When the 2000 census came out, we were able to take stock of where we were. We saw there were patterns at the county level that we hadn’t accounted for."

A curve ball of sorts was thrown 3 years ago, when the 2000 census was conducted. In the 1990 census, respondents were asked to select one racial classification among white, black, Asian or Pacific Islander, American Indian, or Alaska Native. The 2000 census asked respondents to select one or more racial groups, and it separated the Native Hawaiian and other Pacific Islanders group from the Asian group. The result was 31 different ethnic/racial classifications.

A method was needed to bridge these multi-race categories into a sole descriptor to enable the NCI and NCHS to integrate long-term trends in disease rates for single-race groups. To do so, the NCHS developed specialized translational software using information collected as part of its National Health Interview Surveys. In collaboration with NCHS, the Census Bureau also produced a set of year 2000 population estimates that assigned individuals to a single category.

The resulting 2000 estimates were then used to produce an improved set of 1990-2000 population figures. NCI and NCHS are making these bridged-population numbers available on their respective Web sites. These revisions to the population estimates will affect the denominator in all SEER cancer rate calculations for 1990–2000.

"When you look at the broad picture, the problems aren’t apparent," epidemiologist Miller said. "Now people are looking more carefully and in far greater detail than they ever have before. When you look at something under a microscope you discover where the flaws are."

In collaboration with the North American Association of Central Cancer Registries, the Centers for Disease Control, the American Cancer Society, and the NCHS, the NCI is preparing a "Report to the Nation," slated for publication this summer, that will use the updated population information. NCI is also participating in the Cancer Control Planet project, a portal that will provide access to data and resources that can help planners, program staff, and researchers to design, implement, and evaluate evidence-based cancer control programs.

Planners say the site will provide information on the cancer and/or risk factor burden within a given state; identify potential partner organizations that may already be working with high-risk populations; present the latest research findings and recommendations; and make available for downloading evidence-based programs and products.



             
Copyright © 2003 Oxford University Press (unless otherwise stated)
Oxford University Press Privacy Policy and Legal Statement