About the Heart Attack Data

This page provides information about heart attack (also known as an acute myocardial infarction) hospitalization data and measures developed by the Minnesota Environmental Public Health Tracking (MN EPHT) Program. For more information, contact MNPH Data Access.

Information on this page:

What do these data tell us?

  • The numbers and rates of heart attack hospitalizations in Minnesota by year, age group and gender.
  • If heart attack hospitalizations are going up or down over time.
  • If a segment of a population is at higher risk for hospitalization due to heart attack.

How can I use these data?

  • To inform the public about heart attack hospitalizations.
  • For program planning and evaluation by state and local partners.

What can these data not tell us?

  • What causes heart attack, or what leads to heart attack hospitalizations.
  • The total burden of heart attack in a population.
  • The number of people who are hospitalized due to heart attack. Because personal identifiers are removed from the hospital discharge data before analysis, individuals who have multiple hospitalizations cannot be identified.

What is the source of the data?

  • Heart attack 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 report 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.
  • Population-based hospitalization rates are calculated using denominator counts from the US Census. Data from 2000 and 2010 are from the Decennial Census. Data from 2001-2009 and 2011 are from intercensal population estimates.

How are heart attack hospitalizations identified?

  • 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 heart attack, defined by International Classification of Disease 9th Revision, Clinical Modification (ICD-9-CM) code 410.
  • Records with missing county are included in the state count but excluded from county counts.

What is the difference between a number, rate and age-adjusted rate? How would I use them?

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 due to heart attack, but not the number of unique individuals hospitalized.
  • 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 heart attack hospitalizations 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 (in this case 10,000) to make the number more legible.
  • Population-based hospitalization rates are calculated using denominator counts from the US Census. Data from 2000 and 2010 are from the Decennial Census. Data from 2001-2009 are from intercensal population estimates.
  • 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.
  • 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.
    • Heart attack age-adjusted rates are adjusted for adults 35 years and older. The majority of heart attack cases occur in adults 35 years and older.

How can I tell if the underlying rate or percent differs compared to another rate or percent?

  • 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. 95% confidence intervals 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.

What are the limitations of the data?

  • Data in the reports represent the number of hospitalizations due to heart attacks and not the number of individual people hospitalized. Multiple hospital or emergency department admissions by the same patient cannot be identified and are not excluded.
  • Transfers from one hospital to another are not excluded from the data.
  • Since the data only includes those who seek treatment at a hospital, these data are not appropriate for estimating the total burden of heart attacks in a population.
  • 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 analysis 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.

Where can I find more technical information about the data?