National Center for Health Statistics

Technical notes

Nature and sources of data

Provisional drug overdose death counts are based on death records received and processed by the National Center for Health Statistics (NCHS) as of a specified cutoff date, and they are generally updated after the first Sunday of each month. National provisional estimates include deaths occurring within the 50 states and the District of Columbia. NCHS receives the death records from state vital registration offices through the Vital Statistics Cooperative Program (VSCP).

The timeliness of provisional mortality surveillance data in the National Vital Statistics System (NVSS) database varies by cause of death. The lag time (i.e., the time between when the death occurred and when the data were available for analysis) is longer for records where the underlying cause of death was a drug overdose compared with other causes of death (1). Thus, provisional estimates of drug overdose deaths are reported with a 6-month lag time after the date of death.

Provisional death counts presented in this data visualization are for “12-month ending periods,” defined as the number of death records occurring in the 12-month period ending in the month indicated. For example, the 12-month ending period in February 2017 would include deaths occurring from March 1, 2016, through February 28, 2017. The 12-month ending period counts include all seasons of the year and are insensitive to reporting variations by seasonality. Counts for the 12-month ending period in the same month of the previous year are shown for comparison. These provisional counts of drug overdose deaths and related data quality metrics are provided for public health surveillance and monitoring of emerging trends. Provisional drug overdose death data are often incomplete, and the degree of completeness varies by jurisdiction and 12-month ending period. Consequently, the numbers of drug overdose deaths are underestimated based on provisional data relative to final data and are subject to random variation (see Percentage of records pending investigation).

Provisional data are based on available records that meet certain data quality criteria at the time of analysis and may not include all deaths that occurred during a given time period. Therefore, they should not be considered comparable with final data and are subject to change.

Cause-of-death classification and definition of drug deaths

Mortality statistics are compiled in accordance with World Health Organization (WHO) regulations specifying that WHO member nations classify and code causes of death with the current revision of the International Statistical Classification of Diseases and Related Health Problems (ICD). 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 (2).

Drug overdose deaths are identified using underlying cause-of-death codes from the Tenth Revision of ICD (ICD–10): X40–X44 (unintentional), X60–X64 (suicide), X85 (homicide), and Y10–Y14 (undetermined). Drug overdose deaths involving selected drug categories are identified by specific multiple cause-of-death codes. Drug categories presented include: heroin, an illicit (illegally made) opioid synthesized from morphine that can be a white or brown powder or a black sticky substance (T40.1); natural opioid analgesics, including morphine and codeine, and semisynthetic opioids, including drugs such as oxycodone, hydrocodone, hydromorphone, and oxymorphone (T40.2); methadone, a synthetic opioid (T40.3); synthetic opioid analgesics other than methadone, including drugs such as fentanyl and tramadol (T40.4); cocaine (T40.5); and psychostimulants with abuse potential, which includes methamphetamine (T43.6). Categories are not mutually exclusive because deaths may involve more than one drug. Among deaths with an underlying cause of drug overdose, the percentage with at least one drug or drug class specified are identified with at least one ICD–10 multiple cause-of-death code in the range T36–T50.8.

Selection of specific states and other jurisdictions to report

Provisional counts are presented by the jurisdiction in which the death occurred (i.e., the reporting jurisdiction). Data quality and timeliness for drug overdose deaths vary by reporting jurisdiction. Provisional counts are presented for reporting jurisdictions based on measures of data quality: the percentage of records where the manner of death is listed as “pending investigation,” the overall completeness of the data, and the percentage of drug overdose death records with specific drugs or drug classes recorded. These criteria are defined below.

Percent of records pending investigation

In a certain percentage of death records, the manner of death is reported as “pending investigation.” Drug overdose deaths often require lengthy investigations, and death certificates are initially filed with a preliminary or unknown cause of death. When the percentage of records reported as “pending investigation” is high for a given jurisdiction, the number of drug overdose deaths is likely to be underestimated. Drug overdose deaths may be underestimated by roughly 5% using a 1% threshold for percentage pending based on provisional data from the 2015 fourth quarter compared with final data. The degree of underestimation of drug overdose deaths was as high as 30% when the percentage of deaths pending investigation was more than 1%. Thus, jurisdictions are included in Table 2 if 1% or fewer of its records in NVSS are reported as “pending investigation,” following a 6-month lag for the 12-month ending periods included in the dashboard.

Percent completeness

NCHS receives monthly counts of the number of deaths from each jurisdiction (referred to as “control counts”) from state vital registration offices through VSCP. Death records in the NVSS database must have both demographic and coded cause-of-death information. The percent completeness is obtained by dividing the number of death records in the NVSS database for each jurisdiction for each 12-month period by the control counts and multiplying by 100. For more information on completeness, see Technical Notes of the Vital Statistics Rapid Release Program. Jurisdictions are included in Table 2 if the percent completeness was consistently 90% or higher following a 6-month lag for the 12-month ending periods included in the dashboard.

Drug specificity

The percentage of death records in which a specific drug or drug class is identified as involved in a drug overdose death varies by jurisdiction (4). Selected jurisdictions consistently had 90% or more of drug overdose death certificates mentioning at least one specific drug for all of the 12-month ending periods included in the dashboard. Provisional counts of drug overdose deaths where a specific drug or drug class is reported on the death certificate are presented for jurisdictions meeting this threshold and for the United States. Additionally, the percentage of drug overdose death records where at least one drug or drug class is recorded is presented.

As the timeliness and data quality of the drug overdose mortality data improve, the list of included jurisdictions may be periodically re-examined to determine whether additional jurisdictions should be included or excluded based on the criteria described above. Due to reporting variations by jurisdiction, comparisons across selected jurisdictions should not be made. Data quality measures are shown for all jurisdictions in the table below.

Source

NCHS, National Vital Statistics System. Estimates for 2016 and 2017 are based on provisional data. Estimates for 2015 are based on final data (available from: https://www.cdc.gov/nchs/nvss/mortality_public_use_data.htm).

References

1. Spencer MR, Ahmad F. Timeliness of death certificate data for mortality surveillance and provisional estimates. National Center for Health Statistics. 2016.
2. National Vital Statistics System. Instructions for classifying the underlying cause of death. In: NCHS instruction manual; Part 2a. Published annually.
3. Rudd RA, Seth P, David F, Scholl L. Increases in Drug and Opioid-Involved Overdose Deaths—United States, 2010–2015. MMWR Morb Mortal Wkly Rep 65(5051):1445–52. 2016.
4. Warner M, Paulozzi LJ, Nolte KB, Davis GG, Nelson LS. State variation in certifying manner of death and drugs involved in drug intoxication deaths. Acad Forensic Pathol 3(2)231–7. 2013.

Suggested citation

Ahmad FB, Rossen LM, Spencer MR, Warner M, Sutton P. Provisional drug overdose death counts. National Center for Health Statistics. 2017.

Designed by LM Rossen, A Lipphardt, FB Ahmad, JM Keralis, and Y Chong: National Center for Health Statistics.