Methodology

Presently, county-specific measurements of the number of persons with chronic lung disease are not available. In order to assess the magnitude of lung disease at the county levels, this report utilizes a synthetic estimation technique originally developed by the U.S. Census Bureau. This method uses age-specific national or state estimates of diagnosed lung disease to project the prevalence of chronic lung disease and sex-specific age-adjusted state estimates to project the incidence of lung cancer for each county within the United States.

Prevalence Estimates

COPD, Adult Chronic Lung Disease, and Adult and Pediatric Asthma.

The Behavioral Risk Factor Surveillance Survey questionnaire asks respondents “Has a doctor, nurse, or other health professional ever told you that you had any of the following?” followed by a series of conditions. Prevalence rates in this report are based on responses to the questions:

• “(COPD) chronic obstructive pulmonary disease, emphysema or chronic bronchitis?”
• “Asthma?” and “Do you still have asthma?”
• Adult chronic lung disease is defined as answering yes to either the COPD or both asthma questions.

In states fielding the optional child asthma module, adult respondents with one or more children in the household answer the same two asthma questions for the child, if only one, or a randomly selected child, if two or more are reported.

In 2020, the Behavioral Risk Factor Surveillance System (BRFSS) survey found that approximately 23.4 million (9.2 percent) of adults residing in the United States and 7.5 percent of children from twenty-nine states and the District of Columbia reported currently having asthma. About 16.4 million adults (6.5 percent) reported ever being diagnosed with COPD. Close to 34.8 million adults (13.7 percent) reported being diagnosed with chronic lung disease.

Local area prevalence of adult asthma, COPD, and chronic lung disease is estimated by applying age-specific state prevalence rates from the 2020 BRFSS to age-specific county-level resident populations obtained from the U.S. Census Bureau web site. Local area prevalence of pediatric asthma is estimated by applying the most recent state prevalence rates, or if none are available, the national rate from the BRFSS to pediatric county-level resident populations obtained from the U.S. Census Bureau web site. Thereafter, the age-specific prevalence estimates for each county within a state are summed to determine its overall pediatric and adult prevalence.

The prevalence estimates for pediatric and adult asthma are calculated for those under 18 years of age and 18 years of age or older, respectively. Pediatric asthma data from the 2020 BRFSS was available for twenty-nine states and the District of Columbia; 2019 for Illinois and Oregon; 2018 for Maryland; 2016 for Arizona, Oklahoma, and Washington; 2015 for Louisiana; 2014 for Alabama, North Carolina, Tennessee, and West Virginia; 2012 for North Dakota and Wyoming, and 2011 for Iowa; and national data was used for the eight states (Alaska, Arkansas, Colorado, Delaware, Idaho, South Carolina, South Dakota, and Virginia) that had no data available. Data from earlier years was not used due to changes in the 2011 survey methodology.

Asthma and COPD estimates should not be compared to those from 2012 or earlier due to changes in the survey methodology and switch to a different question format, respectively.

Incidence Estimates

Lung Cancer

State- and gender-specific lung cancer incidence rates for 2018 were obtained from StateCancerProfiles.gov, a system that provides access to statistics from both the NCI’s Surveillance, Epidemiology and End Results (SEER) program and the CDC’s National Program of Cancer Registries.

Local area incidence of lung cancer is estimated by applying 2018 age-adjusted and sex-specific incidence rates to 2020 county populations obtained from the U.S. Census Bureau. Thereafter, the incidence estimates for each county within a state are summed to determine overall incidence.

Limitations of Estimates

Since the statistics presented by the BRFSS are based on a sample, they will differ (due to random sampling variability) from figures that would be derived from a complete census or case registry of people in the U.S. with these diseases. The results are also subject to reporting, non-response and processing errors. These types of errors are kept to a minimum by methods built into the surveys. Additionally, a major limitation of both surveys is that the information collected represents self-reports of medically diagnosed conditions, which may underestimate disease prevalence since not all individuals with these conditions have been properly diagnosed. However, the BRFSS is the best available source for asthma and COPD information on the state level. The conditions covered in the surveys may vary considerably in the accuracy and completeness with which they are reported.

Local estimates of chronic lung diseases are scaled in direct proportion to the base population of the county and its age distribution. No adjustments are made for other factors that may affect local prevalence (e.g. local prevalence of cigarette smokers or occupational exposures) since the health surveys that obtain such data are rarely conducted on the county level. Because the estimates do not account for geographic differences in the prevalence of chronic and acute diseases, the sum of the estimates for each of the counties in the United States may not exactly reflect the national or state estimates derived by the BRFSS.