Quarterly Provisional Estimates – Technical Notes – Mortality, 2018 – Quarter 4, 2020
Provisional estimates are based on all complete death records received and processed by the Centers for Disease Control and Prevention’s National Center for Health Statistics (NCHS) as of a specified cutoff date. National provisional estimates include events occurring only within the 50 states and the District of Columbia. NCHS receives the death records and monthly provisional occurrence counts from state vital registration systems through the Vital Statistics Cooperative Program. A complete death record includes both demographic and medical information.
Individual death records are weighted, when necessary, to independent provisional counts of deaths occurring in each state by month. These monthly state-specific provisional counts serve as control totals and are the basis for the record weights used for computing provisional estimates. If the number of complete records is greater than the provisional count received from the state, the state-specific number of complete records is used instead and the weight is set at 1.
Table I shows the percent completeness of the provisional data by month for the United States and each jurisdiction. The percent completeness is obtained by dividing the number of complete records from each state for each month by the corresponding provisional count and multiplying by 100. Although data by place of occurrence are used to evaluate completeness, all rate estimates are for residents of the 50 states and the District of Columbia. State-specific rates may be underestimated based on a small percent of deaths among residents of that state occurring in another state, where completeness may lag.
|District of Columbia||100||100||100||100||100||100||100||100||100||100||100||100|
|New York City2||100||100||100||100||100||100||100||100||100||100||100||100|
1 Excludes New York City.
2 New York City, excluding the rest of the state of New York.
NOTE: Percent completeness equals 100 times the number of death records received at NCHS divided by an individual provisional count of deaths reported by each jurisdiction. NCHS receives the death records and monthly provisional occurrence counts from state vital registration systems through the Vital Statistics Cooperative Program.
When the available data for a specific state and month are less than 50% complete (Table I), they are not used for computing provisional estimates. For these states and months, the number of deaths by underlying cause is imputed based on data from the same state and month in the previous year. These counts are then weighted by the ratio of the state’s population in the same month of both years. For this release, imputation was needed for North Carolina deaths in December 2020.
Mortality statistics are compiled in accordance with World Health Organization (WHO) regulations specifying that WHO member nations classify and code causes of death in accordance with the current revision of the International Statistical Classification of Diseases and Related Health Problems (ICD) (2). ICD provides the basic guidance used in virtually all countries to code and classify causes of death. It provides not only disease, injury, and poisoning categories but also the rules used to select the single underlying cause of death for tabulation from the several diagnoses that may be reported on a single death certificate, as well as definitions, tabulation lists, the format of the death certificate, and regulations on use of the classification. Causes of death for data presented in this report were coded according to ICD guidelines described in annual issues of Part 2a of the NCHS Instruction Manual (3).
Population estimates used for computing rates are postcensal estimates, which originate from the U.S. Census Bureau and are based on the 2010 census. Population estimates used for a single data year are based on population estimates of the same vintage (that is, the same reference year) when available. National rates for 2020 were calculated using the 2020 population estimates, and state-based rates were calculated using 2019 population estimates. Changes in rates between years in part reflect differences between vintages of the population estimates. Quarterly rates are based on the population estimates for the second month of the quarter. Rates for 12-month periods are based on the population estimate at the midpoint of each period.
Death rates are on an annual basis per 100,000 estimated population. Age-adjusted death rates are used to compare relative mortality risks over time; however, they should be viewed as relative indexes rather than as actual measures of mortality risk. They were computed by the direct method; that is, by applying age-specific death rates to the U.S. standard population (relative age distribution of year 2000 projected population of the United States) (4).
Provisional estimates by causes of death are subject to some nonrandom sampling error. This is because the delay in receiving the report of a death depends on the cause of death. The quarterly provisional estimates are based on data that is more incomplete for the most recent months. Causes of death with more delayed reporting tend to be underrepresented in the sample, so the weighting scheme tends to underestimate their rates in the most recent months.
Furthermore, for some deaths, the final cause may not be available at the time the provisional estimates are computed. In those cases, the causes of death may be reported as unknown or pending investigation and coded to the category Other ill-defined and unspecified causes of mortality (ICD–10 code R99), a subcategory of symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (ICD–10 codes R00–R99). In the final data, some of the deaths of unknown cause will be reassigned to specific causes if further, more specific cause-of-death information is provided.
Even if no differential delay occurred in the reporting of final cause of death, some sampling error would still exist for rate estimates, because they are based on incomplete data. A guideline for the size of this sampling error is given by deriving the variation that would occur if the data were missing at random (5).
Partly because of the factors discussed above, these provisional estimates are rarely higher than the true rate. The estimates’ accuracy is stated as how much lower they might be than the true rate, based on experience with recent reporting practices. Because reporting practices have been improving, accuracy of the estimates may be better than recent experience suggests.
For estimates released with a 3-month lag the 3-month estimates are expected to be less than 1.0% below the true rate and estimates for the 12-month period are expected to be less than 0.5% below the true rate. Rate estimates for most external causes of death tend to be less reliable and are released with a longer lag (6). Estimates for homicide, falls for persons aged 65 and over, firearm-related injuries, suicide and unintended injuries are released with a 6 month lag and estimates for drug overdose are released with a 9 month lag. In both cases estimates for 3-month periods are expected to be 1–3% below the true rate and estimates for 12-month periods less than 0.5% below the true rate. Estimates for previously released quarters are revised based on all new data and updates received since the previous release. As a result, the reliability of estimates for a specific quarter will improve with each quarterly release.
Timeliness of death records is similar by sex for all deaths and most causes of deaths (7). Although timeliness of suicide data is initially slightly higher among males than among females, data completeness is similar for male and female suicides at 6-months. As suicide rates are currently presented with a 6-month lag, any difference in the percent of available records by sex would be diminished by the time provisional rates are published.
The timeliness of death certificate data differs by age at the time of death, although data are 90% complete or higher for all age groups for all causes combined (7). There are slight differences by age in timeliness across various causes of death in the first 3 months after a death occurs, with completeness generally lower for heart disease deaths in younger age groups. Completeness for all age groups is generally above 95% at 6 months and beyond.
Accuracy of COVID-19 estimates are assumed to be similar to other natural causes of death. COVID-19 deaths were first reported in 2020, and true accuracy will be assessed once data are finalized.
Most causes of death have a seasonal pattern. This is well-known for influenza but has also been documented for other causes. The bulleted text accompanying estimates for each cause of death compares periods 1 year apart to minimize seasonal influence. Unless otherwise specified, a difference is reported only if statistically significant at the 0.05 level by the z test given in reference 5.
The interactive dashboard was designed by Brian Salant (MirLogic Solutions Corp). Brigham Bastian from the NCHS Division of Vital Statistics provided invaluable support in the development and validation of rate calculations. The Data Acquisition and Evaluation Branch staff of the NCHS Division of Vital Statistics evaluated the quality of and acceptance procedures for the data files on which this report is based. Katherine Irimata from the NCHS Division of Research Methodology evaluated the methodology for calculating relative standard error (RSE) used for statistical testing.
- Kochanek KD, Murphy SL, Xu JQ, Arias E. Deaths: Final data for 2017. National Vital Statistics Reports; vol 68 no 9. Hyattsville, MD: National Center for Health Statistics. 2019. https://www.cdc.gov/nchs/data/nvsr/nvsr68/nvsr68_09-508.pdf
- WHO. International statistical classification of diseases and related health problems, tenth revision (ICD–10). 2008 ed. Geneva, Switzerland. 2009.
- NCHS. National Vital Statistics System. Instructions for classifying the underlying cause of death. In: NCHS instruction manual; Part 2a. Published annually.
- Murphy SL, Xu JQ, Kochanek KD, Bastian B, Arias E, Tejada-Vera B. Deaths: Final data for 2018. National Vital Statistics Reports; vol 69 no 13. Hyattsville, MD: National Center for Health Statistics. 2020. https://www.cdc.gov/nchs/data/nvsr/nvsr69/nvsr69-13-508.pdf
- Hoyert DL, Xu JQ. Deaths: Preliminary data for 2011. National vital statistics reports; vol 61 no 6. Hyattsville, MD: National Center for Health Statistics. 2012.
- Spencer MR, Ahmad F. Timeliness of death certificate data for mortality surveillance and provisional estimates. National Center for Health Statistics. January 2017.
- Ahmad FB, Dokpesi P, Escobedo L, Rossen L. Timeliness of death certificate data by sex, age, and geography. Vital Statistics Rapid Release; no 9. Hyattsville, MD: National Center for Health Statistics. June 2020. Available from: https://www.cdc.gov/nchs/data/vsrr/VSRR009-508.pdf.