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Infant Mortality: Notes & Sources


Confidence interval (also called "error bar") is the range of values that includes the true value 95% of the time. If the confidence intervals of two groups do not overlap, the difference between groups is statistically significant (meaning that chance or random variation is unlikely to explain the difference).   

Health Reporting Areas (HRAs): In 2011, new King County Health Reporting Areas (HRAs) were created to coincide with city boundaries in King County.  HRAs are based on aggregations of U.S. Census Bureau-defined blocks.  Where possible, HRAs correspond to neighborhoods within large cities, and delineate unincorporated areas of King County. The new HRAs were designed to help cities and planners as they consider issues related to local health status or healthy policy.  HRAs are used whenever we have sufficient sample size to present the data.

Healthy People 2020 is a set of national 10-year objectives for health promotion and disease prevention.  According to Assistant Secretary for Health Howard K. Koh, “Healthy People is the nation’s roadmap and compass for better health, providing our society a vision for improving both the quantity and quality of life for all Americans.”  The Healthy People goal is to reduce infant mortality to 6.0 per 1,000 births by 2020.

Infant mortality:  The infant mortality rate for a given year represents the number of deaths to King County residents younger than 1 year of age per 1,000 live births to King County residents during the same year.  For example, the rate for 2010 was 4.2 deaths per 1,000 live births.

King County regions: The geographic boundaries of the four King County sub-regions (North, Seattle, East, and South) are defined by the aggregation of Health Reporting Areas.

Neighborhood poverty levels are based on the proportion of households in a Census tract in which annual household income (as reported in the U.S. Census Bureau’s American Community Survey) falls below the federal poverty threshold.  For a family of four in 2010, the poverty threshold was $22,050; in 2012, it was $23,681.

  • High poverty: 20% or more households in the neighborhood below poverty threshold.
  • Medium poverty: 5% to 19% of households below poverty threshold.
  • Low poverty: fewer than 5% of households below poverty threshold.

Race/Ethnicity: Federal standards mandate that race and ethnicity (Hispanic origin) are distinct concepts requiring 2 separate questions when collecting data from an individual. "Hispanic origin" is meant to capture the heritage, nationality group, lineage, or country of birth of an individual (or his/her parents) before arriving in the United States. Persons of Hispanic ethnicity can be of any race. Communities Count's terms for racial/ethnic groups are derived from those used by the U.S Census Bureau in 2010.

  • Communities Count terms:  Hispanic, Black, American Indian/Alaska Native (AIAN), Asian, Native Hawaiian/Pacific Islander (NHPI), White, and Multiple Race (Multiple). Persons of Hispanic ethnicity can be of any race and are included in other racial categories. Racial/ethnic groups are sometimes combined when sample sizes are too small for valid statistical comparisons of more discrete groups. 
  • 2010 Census terms: Hispanic or Latino, Not Hispanic or Latino, White alone (Not Hispanic or Latino),  Black or African American, American Indian or Alaska Native, Asian, Native Hawaiian or Other Pacific Islander, White, Some Other Race, and Two or More Races.
  • In this report, race is that of mothers who report a single race; mothers who reported more than one race are included in the “multiple race” category.  Consistent with federal standards on the reporting and collection of data on race and ethnicity, revised racial category data are available for infant mortality in Washington State beginning in 2004.  Mothers can now report more than one race; and separate categories exist for Asians and for Native Hawaiians and other Pacific Islanders. 

Rolling averages:  When the frequency of an event varies widely from year to year, rates are sometimes aggregated into averages – often in 3-year intervals – to smooth out the peaks and valleys of the yearly data. For example, for events occurring from 2001 to 2010, rates may be graphed as three-year rolling averages: 2001-2003, 2002-2004…2008-2010. Adjacent data points will contain overlapping years of data. Statistical tests comparing data points with overlapping times are not appropriate.


Data were averaged:

  • Over 3 years in “rolling averages” for trend graphs.
  • Over 5 years to enable more robust comparisons across geographic and demographic groups.

Statistical Significance: Unless otherwise noted, any difference mentioned in the text is statistically significant (unlikely to have occurred by chance).

Trend graphs for all sub-populations are shown as “rolling averages” (see definition above) that smooth the plotted lines, making it easier to observe changes – or the absence of changes – over time. For relatively small populations, slight changes in the number of events can cause the rate to fluctuate substantially, creating jagged lines of statistical “noise.”

Data Sources

Data on infant mortality in King County is collected through birth certificate and infant death certificate records by the Washington State Department of Health, Center for Health Statistics.

Other Sources

City Health Profiles provide demographic and health information for 25 geographic areas in King County – mostly large cities (e.g., Seattle, Bellevue), groups of small cities (Bothell/Woodinville), or combinations of cities with nearby unincorporated areas (e.g., Renton/Fairwood). Each report has seven sections:

  • Demographics
  • General health status
  • Leading causes of death
  • Health risk factors and chronic diseases
  • Injury and violence-related mortality
  • Maternal and infant health
  • Access to care and preventive services

Global trends in relationship of GDP per capita to child mortality:

Healthy People 2020:  U.S. Department of Health and Human Services (December 2, 2010). HHS announces the nation’s new health promotion and disease prevention agenda.

Maps of King County covering a wide range of topics can be accessed at  Maps most immediately relevant to Communities Count are under the headings of Community data & demographics, Public health, and Environment & natural resources, but other maps should be useful as well (farmers markets, transit routes, walking and biking routes, parks, traffic counts, etc.).

Racial disparities in infant mortality: King County, 1980-1998 (August 2000)Public Health – Seattle & King County, Public Health Data Watch, Vol. 4(3). (go to August 2000), accessed on 03/01/2013.