Glossary

Terms of art, each defined once in plain language. In the chapters, a marked term shows its definition on hover or focus.

Age-adjusted rate: A rate recalculated as if every place had the same mix of ages, so that places can be compared without the effect of having older or younger residents.
Area Deprivation Index (ADI): A score that ranks neighborhoods by income, education, employment and housing conditions drawn from the American Community Survey. In this book a higher national percentile means a more deprived neighborhood.
Bootstrap interval: A range for an estimate found by recomputing it on many random resamples of the data and reading the range from the results. It shows how much the estimate would vary from sample to sample.
Cantril ladder: A survey question that asks people to place their life on a ladder whose bottom step is the worst possible life and whose top step is the best possible. It measures how people evaluate their life as a whole, not how they felt yesterday.
Census tract: A small area drawn by the Census Bureau to stand in for a neighborhood. Boundaries are redrawn after each decennial census.
Complete county: A county whose death count is published in every year of a window, possibly as zero, so its rate over the window is exact. Counties that are complete are selected by their counts, so as a group they are not typical of counties their size.
Crude rate: Deaths or births divided by the population, with no adjustment for age. A place with older residents has a higher crude death rate even if health at each age is the same.
Design effect: How much a survey's sampling design (strata, clusters and unequal weights) widens an interval compared with a simple random sample of the same size. This book computes intervals from the design itself rather than inflating them by an assumed design effect.
Ecological inference: Drawing conclusions about individuals from data about places or groups. A pattern across counties need not hold for the people inside them.
Economic connectedness: A measure of friendship across class lines, based on the share of high-status friends among people below the median in socioeconomic status. It is scaled so that friendships mixing in proportion to the population give the reference value.
EITC: The Earned Income Tax Credit, a refundable federal tax credit for low and moderate income workers. It grows with earnings up to a limit and then phases out.
Fixed effects: A regression adjustment that gives each group, such as each county, its own baseline. The estimate then rests on differences within groups.
HOLC grade: A letter from A to D that the Home Owners' Loan Corporation gave neighborhoods on its 1930s maps, with A labeled best and D hazardous. The maps are known as redlining maps.
Income rank (kfr): The position that adult children reach in the national distribution of household income, from the lowest rank to the highest, averaged over children who grew up in a place with parents at a stated income level. The Opportunity Atlas labels this measure kfr.
Infant mortality rate: The number of babies who die before their first birthday for every thousand live births.
Interquartile range: The distance between the first quartile and the third quartile of a set of values. It describes the spread of the middle of a distribution and is not moved by extreme values.
Inverse care law: The pattern that people who need medical care most tend to receive the least of it. The physician Julian Tudor Hart named it in 1971.
K-means: A method that sorts places into a chosen number of groups so that places in a group resemble one another on the measures used. The analyst sets the number of groups.
Life expectancy at birth: The average number of years a newborn would live if death rates at every age stayed as they were in the period measured. It summarizes the death rates of a period and is not a forecast for any child.
Low birthweight: A live birth weighing less than 2,500 grams, the cutoff used in vital statistics.
MAUP (modifiable areal unit problem): The same data can show different patterns depending on how the map is divided, for example into tracts, counties or states.
Modeled estimate: A figure produced by a statistical model instead of a direct count or measurement, usually for small areas where direct data are thin, borrowing strength from surveys, neighboring areas or other data. Neighboring areas can share errors, so single extremes call for caution.
National percentile: A neighborhood's position in the national ordering, given as the share of all neighborhoods that fall below it. A higher percentile means a higher value than more of the rest of the country.
OASDI: Old-Age, Survivors and Disability Insurance, the Social Security programs that pay retirement, survivor and disability benefits.
Population-weighted: Averaged so that each place counts in proportion to its number of residents, which lets a large county move the result more than a small one. An unweighted average counts every place equally.
Preterm birth: A birth before 37 weeks of pregnancy.
Price-standardized spending: Medicare spending adjusted to remove differences in local prices and payment rules, so that counties are compared on the care paid for rather than on local prices. It does not adjust for how sick the beneficiaries are.
Principal components: A method that combines many correlated measures into a few summary scores, ordered by how much of the variation among places each captures. The first component is the single weighted combination that captures the most.
SD units (SEDA): Test scores stated in units of the typical spread of scores around the national average, so that a score reads as the number of such spreads above or below the national average. SEDA also reports scores in grade levels, which are a separate scale.
Silhouette: A score for how well a place fits the group it was assigned in a clustering. Higher values mean the place sits close to its own group and far from the others.
Suppression: The withholding of a number because the count behind it is too small to publish without risking the identification of a person. A suppressed value is missing, not zero.
Survey weights: Numbers attached to survey respondents that say how many people in the population each one represents, so that results describe the whole population and not only the people who answered.
USALEEP: The U.S. Small-area Life Expectancy Estimates Project, a National Center for Health Statistics release of life expectancy at birth for most census tracts. It covers deaths from 2010 to 2015 only and has not been updated.
Weathering: The hypothesis that chronic stress from disadvantage and discrimination wears down health faster, so that the same outcomes appear at younger ages in affected groups. Arline Geronimus proposed it in studies of birth outcomes.
ZCTA: ZIP Code Tabulation Area, the Census Bureau's approximation of a ZIP code as a set of census blocks. It lets census data be reported by ZIP code, though some ZIP codes have no matching ZCTA.
ZIP code: A postal delivery code assigned by the U.S. Postal Service. It describes mail routes, not a fixed area, so ZIP-keyed data must be matched to ZCTAs before they are mapped with census data.