For all medication-round fills, except for drugs determined to be a confidentiality risk (see below), RXNDC reports the National Drug Code (NDC) of the prescribed medicine. The NDC is provided during the pharmacy component of the MEPS survey. In cases where the NDC provided by the pharmacy is not valid, a secondary data source is used to impute a valid value for that prescribed medicine. See the comparability tab for more information about how these cases are handled over time. See also RXNAME and RXDRGNAM for additional information about prescribed medication-round fill attributes.
In most cases, each prescribed medicine is associated with one RXNDC value, however, each fill of a prescribed medicine can have a unique RXNDC value in cases where the medication's form, strength, manufacturer, or package size differ across fills. Thus, a prescribed medicine may have only been reported once in the household component but may be represented by multiple medication-round fills with unique RXNDC values in the data.
For 1996-2008 samples, RXNDC was used to link drugs across rounds. Beginning in 2009, DRUGID was introduced as the "prescribed medicine drug-level ID" and replaced RXNDC as the variable used to link drugs over time. See DRUGID for more information about linking drugs across MEPS rounds and see MEPSDRUGID for more information about linking drugs across MEPS panels.
A drug can pose a confidentiality risk for several reasons. Examples include orphan drugs, drugs that are estimated to be used by fewer than 200,000 people, or drug names that provide identifying information about the pharmacy or respondent. An orphan drug is a drug that treats a rare disease or condition but has been discontinued because there is little or no economic incentive to continue development or production. See Rare Diseases at the FDA for more information about how these drugs are designated and the effort to financially support their development and production under the Orphan Drug Act. See the codes tab for more detailed information about how cases that pose a confidentiality risk are handled in the data.
IPUMS MEPS reports the universe for each variable based on a thorough review of the original MEPS documentation. Investigating the data may reveal cases that do not meet the stated universe. Users are encouraged to validate universes for their analyses.
RXNDC is on the medication-round fill record (see RECTYPE for more details on the different record types in IPUMS MEPS). Variables offered on the medication-round fill record through IPUMS MEPS are derived from the prescribed medicines file provided by AHRQ. Please see our overview of the event, medical conditions, and prescribed medicines variables, including how those variables are offered through IPUMS MEPS, and general considerations to keep in mind when conducting analyses using these variables.
RXNDC is an 11-digit string variable. The first 5 digits of the NDC code report the manufacturer of the prescribed medicine. The next 4 digits of the NDC code report the form and strength of the prescription. The last 2 digits of the NDC code report the package size from which the prescription was dispensed.
In the case that a prescription drug name was determined to be a confidentiality risk, RXNDC is assigned a value of 0: "Not in Universe." Users should note that in the original documentation for 1996-2017 samples, this value was -9: "Not Ascertained," and in the original documentation for 2018-onward samples, this value was -15: "Cannot be Computed."
For 1996-2004 samples, AHRQ was not able to release imputed RXNDC values on the public-use files due to their licensing agreement with the NDC proprietary database. For those prescribed medicines with imputed NDC values, the pharmacy reported name of the prescription (RXNAME) and the original RXNDC value are provided on the public-use files to allow users to impute their own values for these years. The imputed values can be accessed through the AHRQ data center.
- 1996-2021: All medication-round fills, except cases in which the NDC value is determined to be a confidentiality risk.
- 1996-2021 : PERWEIGHT