About the COPD Data

This page provides information about chronic obstructive pulmonary disease (COPD) data and measures developed by the Minnesota Environmental Public Health Tracking (MN EPHT) Program. For more information, contact MNPH Data Access.

  • The prevalence of COPD in Minnesota by age group.
  • The numbers and rates of COPD hospitalizations or deaths in Minnesota by year, age group, race/ethnicity and gender.
  • If COPD hospitalizations and deaths are going up or down over time.
  • If a segment of a population is at higher risk for COPD hospitalizations or deaths.
  • To inform the public about COPD prevalence, hospitalizations, and deaths.
  • For program planning and evaluation by state and local partners.
  • What causes COPD, or what leads to hospitalizations and deaths.
  • The total burden of COPD in a population.
  • The number of people who are hospitalized due to COPD. Because personal identifiers are removed from the hospital discharge data before analysis, individuals who have multiple hospitalizations cannot be identified.
  • COPD prevalence data are from the Behavioral Risk Factor Surveillance System (BRFSS), administered annually by the Minnesota Center for Health Statistics in collaboration with the Centers for Disease Control and Prevention (CDC). The BRFSS is administered by telephone to a sample of Minnesotans that is representative of the state population. To learn more about BRFSS, including survey methodology (i.e. how participants are chosen) and full length questionnaires, visit CDC BRFSS.
  • COPD hospitalization data are extracted from Minnesota Hospital Discharge Data (MNHDD), which is maintained by the Minnesota Hospital Association (MHA).
    • MHA represents Minnesota's hospitals and health systems. Hospitals submit inpatient discharge data to MHA using a standardized billing form. In 2010, 99.3% of all hospitals in the state reported hospital discharge data to the MHA, representing 99.4% of all licensed beds in the state.
    • MHA began data-sharing agreements with several states in 2005. Minnesota residents receiving care from hospitals from the participating border states of North Dakota, South Dakota and Iowa are also included in this analysis beginning in 2005.
    • MHA data are periodically revised by the MHA to reflect more complete and accurate discharge information.
  • COPD mortality data are extracted from the Centers for Disease Control and Prevention Wide-ranging OnLine Data for Epidemiologic Research (CDC WONDER) database, Underlying Cause of Death, 1999-2014.
  • Population-based hospitalization and death rates are calculated using denominator counts from the U.S. Census and American Community Survey.
  • For Behavioral Risk Factor Surveillance System purposes, survey respondents are classified as having COPD if they respond 'yes' to the question, 'Has a doctor, nurse, or other health professional ever told you that you have Chronic Obstructive Pulmonary Disease or COPD, emphesyma or chronic bronchitis?'.

Hospitalizations

  • Minnesota residents who are discharged from a hospital in Minnesota or the bordering states of North Dakota, South Dakota or Iowa.
  • Primary discharge diagnosis of COPD, defined by International Classification of Disease 9th Revision, Clinical Modification (ICD-9-CM) codes 490, 491, 492 or 496. Also included, primary diagnosis of 493.2 when 490, 491, 492 or 496 is present in any of the secondary diagnosis fields.
  • Because COPD is a disease of adults, only ages 25 and older are included in summary rates for the population. The majority of COPD cases occur in older adults. However, 0-24 and 25-44 age groups are included in age-specific COPD rates because some cases do occur in younger adults.
  • Records with missing county are included in the state count but excluded from county counts.

Deaths

Number:

  • If you want to understand the magnitude or how big the overall burden is, then use the number.
  • The number indicates the total number of hospitalizations or deaths due to COPD.
  • To protect an individual's privacy, hospitalizations counts from 1 to 5 are suppressed if the underlying population is less than or equal to 100,000.

Rate:

  • If you want to understand the probability or what is the underlying risk in a population, then use a rate and confidence interval.
  • A rate is a ratio between two measures with different units. In our analysis a rate is calculated using a numerator, the number of COPD hospitalizations or deaths during a period of time, divided by a denominator, the number of people at risk in a population during the same period of time. This fraction is then multiplied by a constant to make the number more legible.
  • Population-based hospitalization and death rates are calculated using denominator counts from the U.S. Census and American Community Survey.
  • To protect an individual's privacy, rates based on hospitalization counts from 1 to 5 are suppressed if the underlying population is less than or equal to 100,000.
  • Hospitalization rates based on counts of 20 or less are flagged as unstable and should be interpreted with caution. These rates are unstable because they can change dramatically with the addition or subtraction of one case.
  • A rate is considered crude if it is not adjusted for the age or sex distribution.
  • Age-adjusted rate:
    • Age-adjusted rates are useful when comparing the rates of two population groups that have different age distributions
    • A weighted average, called the direct method, is used to adjust for age in this analysis. Age specific rates in a given population are adjusted to the age distribution in a standard population by applying a weight. The U.S. 2000 Standard population is used as the basis for weight calculations.
    • COPD age-adjusted hospitalization rates are adjusted for adults 25 years and older. Age-adjusted death rates are adjusted for all ages.
  • Assessing the confidence interval for the percent or rate is one approach to determine whether there are differences over time or compared to another location. If they do not overlap then they differ. Although it is not a true statistical test, it is a commonly accepted way to compare percents or rates and tends to be more conservative than statistical testing.
  • A confidence interval for a rate is a measure of reliability. In this analysis, 95% confidence intervals were calculated. A 95% confidence interval is the interval within which the true value of the rate would be expected to fall 95 times out of 100. When the number of events is fewer than 100, the 95% confidence interval is calculated based on the inverse gamma distribution in this analysis. When the number of events is 100 or greater, the 95% confidence interval is calculated based on normal approximation.

Prevalence:

  • The Behavioral Risk Factor Surveillance System administers questionnaires to a sample of Minnesota adults in households. It does not represent all Minnesota adults, such as those in long-term care facilities, nursing homes, the military or correctional institutions.
  • BRFSS is a telephone survey and therefore does not reach adults who have no telephone. As with most surveys that rely on telephone interviewing, some subgroups, such as specific racial or ethnic minority communities, are likely to be underrepresented.

Hospitalizations:

  • Data represent the number of hospitalizations due to COPD and not the number of individual people hospitalized. Multiple hospital admissions by the same patient cannot be identified, and are not excluded.
  • Since only those with the most severe symptoms of COPD are hospitalized, hospitalization data are not appropriate for estimating the total burden of COPD.
  • Hospitalization measures on MN Public Health Data Access include discharges of Minnesota residents from hospitals in the border states of North Dakota, South Dakota and Iowa, beginning in year 2005. County-level analyses are only from 2005 onward because the addition of out-of-state hospitalizations greatly affects the rate of some counties.
  • Minnesota residents discharged from Wisconsin hospitals are not included, so hospitalization rates for counties in which residents are likely to receive care from Wisconsin may be underestimated. Rates for counties in which residents are likely to visit hospitals that do not submit data to the Minnesota Hospital Association (e.g., Veteran's Administration or Indian Health Services hospitals) may also be artificially low.
  • There is usually a two year lag period before hospitalization data are available.

Mortality:

  • To learn more about COPD data and measures developed by the MN Environmental Public Health Tracking Program, contact MNPH Data Access.