• Component Description
• Eligible Sample
• Interview Setting and Mode of Administration
• Quality Assurance & Quality Control
• Data Processing and Editing
• Analytic Notes
• References
• Codebook
  • SEQN - Respondent sequence number
  • RXDUSE - Taken prescription medicine, past month
  • RXDDRUG - Generic drug name
  • RXDDRGID - Generic drug code
  • RXQSEEN - Medicine container seen by interviewer
  • RXDDAYS - Number of days taken medicine
  • RXDRSC1 - ICD-10-CM code 1
  • RXDRSC2 - ICD-10-CM code 2
  • RXDRSC3 - ICD-10-CM code 3
  • RXDRSD1 - ICD-10-CM code 1 description
  • RXDRSD2 - ICD-10-CM code 2 description
  • RXDRSD3 - ICD-10-CM code 3 description
  • RXDCOUNT - Number of prescription medicines taken
• Appendix: ICD-10-CM codes assigned to reasons for use reported by participants

National Health and Nutrition Examination Survey

2015-2016 Data Documentation, Codebook, and Frequencies

Prescription Medications (RXQ_RX_I)

Data File: RXQ_RX_I.xpt

First Published: January 2019

Last Revised: NA

Component Description

The Dietary Supplement and Prescription Medication section of the Sample Person (SP) Questionnaire collects information on: 1) dietary supplements, 2) nonprescription antacids, 3) prescription medications, and 4) preventive aspirin use.

The Prescription Medications Questions (variable name prefix RXQ) provides personal interview data on the use of prescription medications during a one-month period prior to the participant’s interview date. The NHANES 2015–2016 prescription medication questions are similar to the NHANES 1999–2014 and NHANES III (1988–1994) prescription medication questions.

Eligible Sample

All survey participants were eligible.

Interview Setting and Mode of Administration

The RXQ was asked, in the home, by trained interviewers using the Computer-Assisted Personal Interview (CAPI) system. Participants over 16 years of age answered for themselves; a proxy provided information for survey participants who were under 16 years of age and for those who could not answer themselves.

The Interviewer Procedure Manuals and Survey Questionnaires can be found on the NHANES website. The Dietary Supplement and Prescription Medication section of the SP Questionnaire are at:
https://wwwn.cdc.gov/nchs/data/nhanes/2015-2016/questionnaires/DSQ_I.pdf.

Quality Assurance & Quality Control

Data were routinely examined for discrepancies and erroneous entries. All drug names entered by the interviewer were compared to the medication names selected from the database. Review of the 2015–2016 data found that 95% of all reported drugs were automatically matched to the data collection drug database. This included 81% exact matches, and 14% similar matches. After the data collection, all similarly matched drug names were reviewed and edited if either entered or selected drug names were incorrect. The 5% that were not matched to the drug database were also reviewed and edited. The most common reasons for a non-match were incorrect spelling of the drug, insufficient detail to identify the drug, or reporting of a nonprescription product that was not in the drug database.

Similar to the previous 2013–2014 survey cycle, a list of possible reasons for use assigned to each drug was incorporated into the computer to assist the data collection. Review of the 2015–2016 data found that 85% of all reported reasons were selected from the list. The 15% that were entered in the reason field were edited, at NCHS, after data collection.

Data Processing and Editing

Data Collection Methods

During the household SP interview, survey participants are asked if they have taken medications in the past 30 days for which they needed a prescription. Those who answer “yes” are asked to show the interviewer the medication containers of all the products used. For each medication reported, the interviewer enters the product’s complete name from the container into a computer. If no container is available, the interviewer asks the participant to verbally report the name of the medication.

When the interviewer enters the medication name into the computer, the name is automatically matched to a prescription drug database on the computer to identify an exact match or similar text matches (refer below for details on the prescription medication database). The interviewer then selects the best match from a drug list of possible matches. The original product entered by the interviewer and the product selected from the computer drug list are saved as separate variables for quality control purposes. If an exact or similar match of the medication cannot be found in the database, the interviewer is instructed to select “drug not found on list.”

Participants were also asked how long they have been taking the medication and the main reason for use. A list of possible reasons (indications of medication use and possible off-label use) pre-assigned to each selected drug is displayed on the computer. The interviewer is instructed to select up to 3 reasons from the reason list that best match to the main reason described by the participant. If an appropriate reason is not available, the interviewer is instructed to enter the main reason as described by the participant.

The NHANES 2015–2016 RXQ can be accessed in the Dietary Supplements and Prescription Medications section of the SP Questionnaire:
https://wwwn.cdc.gov/nchs/data/nhanes/2015-2016/questionnaires/DSQ_I.pdf.

Prescription Medication Questions Included in this Data Release

• Was any prescription medication taken in the past 30 days?
• Medication name
• Was medication container seen by interviewer?
• How long was medication taken?
• What is the main reason for which you use medication?
• Number of prescription medications taken?

Prescription Medication Database for Data Collection

NCHS used Lexicon Plus®, a proprietary database of Cerner Multum, Inc. to assist in data collection. Lexicon Plus® is a comprehensive database of all prescription and some nonprescription drug products available in the U.S. drug market. For NHANES, the Lexicon Plus® files were modified and uploaded to a laptop computer and incorporated into a search engine for use by interviewers. The computer file was updated at the beginning of each survey year to incorporate changes to Lexicon Plus® and include products approved and available to the U.S. public in the prior year.

Data Editing

General editing of data

When a variable was modified globally, as part of the editing process, the third letter in the variable name was changed from a Q (i.e., RXQ) to a D (i.e., RXD). For example, variables that were obtained from an external drug database will have the letter “D” in the third position of the variable name.

Prescription medications incorrectly reported in other subsections of questionnaire

Prescription antacids that were incorrectly reported in the nonprescription antacid section of the questionnaire were removed from the antacid file and added to the prescription medication file.

Prescription supplements are released in the Dietary Supplements Data file. Some prescription medications were mistakenly recorded in the dietary supplement section. These were removed from that file and added to the prescription medication file. Any prescription dietary supplement that was incorrectly reported in the prescription medication section was removed from the prescription medication section and moved to the dietary supplement section. The following products were moved to the Dietary Supplements files (DSQ):

• All calcium products except calcium acetate
• All fluoride products except those in topical gel or cream forms (e.g., stannous fluoride)
• All vitamins except the injection form of vitamins
• Over-the-counter niacin, niacinamide, nicotinic acid, and fish oil

All prescription niacin, fish oil, potassium, and sodium products were retained in the prescription medication file. Injectable prescription vitamin B or iron were also retained in the prescription medication file.

Products reported in the prescription medication section that were only available as an over-the-counter product during 2015–2016 were removed from the prescription medication file, except over-the-counter insulin, and products containing pseudoephedrine.

Specific variables and edits

RXDUSE: Have you taken or used any prescription medicines in the past month?

This variable was the lead-in question to the series of questions on prescription medication use. It accounts for all prescription medications except prescription dietary supplements, which are included in the dietary supplement files (DSQ). A small number of persons refused to answer this question (coded 7) or did not know whether they used a prescription medication in the past month (coded 9).
This variable was edited and takes into account prescription medications reported in this section as well as prescription medications moved into this file from the dietary supplements or nonprescription antacids sections of the questionnaire.

RXDCOUNT: The number of prescription medicines taken?

This variable was computed at NCHS and represents the total number of prescription medications reported by the participant, including those drugs identified as unknown (RXDDRUG = 55555). The count has been adjusted for all prescription medications moved into and those moved out of the prescription medication section. However, the count is not a comprehensive count of all prescription medications used by a participant because prescription dietary supplements are part of the dietary supplement section. There were also participants who reported the use of a prescription medication in the past month (RXDUSE = 1) but did not know the name of the medication (RXDDRUG = 99999) or refused to report the name of the medication (RXDDRUG = 77777). Each product reported as “refused” or “don’t know” is still included in the total count of prescription medications used under RXDCOUNT.

RXQSEEN: Medicine container seen by interviewer?

There was no editing of this variable.

RXDDAYS: For how long have you been taking this medicine?

This variable was created from a two-part (number and unit) question and indicates how long the participant reported taking each prescription medication. Responses were recorded in days, weeks, months, and years. To facilitate analysis, all answers were converted to days using conversion factors of 7 days per week, 30.4 days per month, and 365 days per year. The length of use was top coded to 21900 days. There were persons who reported the use of a prescription medication but did not know how long they had been using the medication (RXDDAYS = 99999) or refused to report the length of use (RXDDAYS = 77777). There were also persons who reported the use of a prescription medication but did not report the length of use. RXDDAYS is missing for those persons.

Drug Database for Data Release

NCHS used Lexicon Plus®, a proprietary database of Cerner Multum, Inc. to assist with data editing and release. The December 2016 Multum Lexicon database was used for creating the RXQ_RX_I data release file. For additional information, refer to the RXQ_DRUG documentation.

Creation of additional data release variables

RXDDRUG: Generic drug name

All reported drug names were converted to a standard generic drug name for data release. For multi-ingredient products, the ingredients were listed in alphabetical order (i.e., Acetaminophen; Codeine).

There were participants who reported the use of a prescription medication but did not know the name of the drug or refused to report the name. These entries were coded as don’t know (99999) and refused (77777), respectively. There were also medications reported with insufficient detail to accurately identify the exact product, but there was some information about the therapeutic class of the drug. These products have been released with Multum’s therapeutic category name followed by “- unspecified” (e.g., anti-infective - unspecified; hormones/hormone modifiers - unspecified). The names of a limited number of reported drugs could not be identified by NCHS as a known prescription product. These entries were counted as prescription medications, since there is no evidence that they are not, and have been coded as 55555, unknown drug.

RXDDRGID: Generic drug code

Each generic drug name is associated with a unique generic drug code from Multum’s Lexicon Drug Database. Multum's generic drug code is always beginning with a "d". There were some drug names reported by NHANES’ participants that were not found in the Lexicon drug database. These have been assigned unique drug codes beginning with an “a” or “h”. Unspecified products with known therapeutic action have drug codes beginning with a “c” and are followed by their respective Multum therapeutic category code. RXDDRGID is missing for unknown drugs (55555), refused (77777), or don’t know (99999) RXDDRUG entries.

Therapeutic class codes associated with a drug are found in a separate data release file, RXQ_DRUG.

International Classification of Disease, Tenth Revision, Clinical Modification (ICD-10-CM) Code for Data release

The ICD-10-CM is a system used by physicians and other healthcare providers to classify and code all diagnoses, symptoms and procedures recorded in conjunction with hospital care in the United States. To facilitate data analysis, NCHS used ICD-10-CM codes (https://www.icd10data.com/ICD10CM/Codes) to classify the health problems participants reported as the main reason for taking the prescription medication. Thus, the associated ICD-10-CM codes were based on participant reported reason and not directly reported by a doctor or other health professional or by a review of the medical record. ICD-10-CM diagnosis codes have between 3 and 7 characters. In general, the self-reported health problems were coded to the fourth digit ICD-10-CM level of specificity. However, in some cases only the first three digits as the heading of a category of codes was used; and in other cases the six digits ICD-10-CM level of specificity was used. See the Appendix for a list of ICD-10-CM codes and description assigned to reasons for use reported by NHANES participants.

Reason for use (as reported by participant) data release variables

RXDRSC1-- RXDRSC3: ICD-10-CM code

The participants’ reported reasons were converted to an ICD-10-CM code for data release. Up to a maximum of 3 ICD-10-CM codes were used if multiple reasons were reported for a specific medication use. When reported reason was for disease prevention, an appropriate ICD-10-CM code followed by a letter "P" was used. (e.g., A49.9P Prevent bacterial infection; D75.9P Prevent blood clots). When reported reason was not specific enough to be assigned an ICD-10-CM code for the subtype of disease, an ICD-10-CM code for a most common subtype of disease was used (e.g., E11 for diabetes; E78.0 for high cholesterol). When reported reason did not indicate a single episode or recurrent, an ICD-10-CM code for a single episode was used (e.g., F32.9 for depression). When reported reason was a symptom due to an underline disease, a disease code was used (e.g., I51.9 for fluid retention due to heart problem; K76.9 for fluid retention due to liver problem).

There were participants who reported the use of a prescription medication but did not know why they took it or refused to report the reason for use. These were coded as 99999, don’t know, and 77777, refused, respectively. There were a number of reported reasons that could not be converted to an appropriate ICD-10-CM code. These entries have been grouped into unspecified ICD-10-CM codes or coded as 55555, unknown. A few rare diseases were also coded as 55555, unknown.

RXDRSD1-- RXDRSD3: ICD-10-CM code description

Each ICD-10-CM code is associated with a description (diseases, symptoms, health status, and so on). RXDRSD1 is missing for unknown reasons (55555), refused (77777), or don’t know (99999) RXDRSC1 entries.

There are two files related to the prescription drug data. The contents of each file are described below. The files can be linked by the variable RXDDRGID.

The file named RXQ_RX_I contains data on all survey participants and their use of a prescription drug. Participants who reported the use of multiple prescription drugs will have multiple records, that is, a record for each drug.

The file named RXQ_DRUG contains therapeutic drug class information on all drugs reported by NHANES participants from 1988–1994 through 2015–2016. It contains drug (up to 4) and ingredient (up to 6) therapeutic category codes for each drug. It also has a variable that identifies if the drug is made of a single ingredient or multiple ingredients.

RXQ_RX_I: Participant’s Use of Prescription Drug(s)

Variable Name	Label
SEQN	Respondent sequence number
RXDUSE	Taken prescription medicine, past month
RXDDRUG	Generic drug name
RXDDRGID	Generic drug code
RXQSEEN	Medicine container seen by interviewer
RXDDAYS	Number of days taken medicine
RXDRSC1	ICD-10-CM code 1
RXDRSC2	ICD-10-CM code 2
RXDRSC3	ICD-10-CM code 3
RXDRSD1	ICD-10-CM code 1 description
RXDRSD2	ICD-10-CM code 2 description
RXDRSD3	ICD-10-CM code 3 description
RXDCOUNT	Number of prescription medicines taken

RXQ_DRUG: Drug Information

Variable Name	Label
RXDDRGID	Generic drug code
RXDDRUG	Generic drug name
RXDINGFL	SINGLE/MULTIPLE INGREDIENT DRUG
RXDDCI1A	DRUG CATEGORY ID - CAT 1, LEV 1
RXDDCI1B	DRUG CATEGORY ID - CAT 1, LEV 2
RXDDCI1C	DRUG CATEGORY ID - CAT 1, LEV 3
RXDDCI2A	DRUG CATEGORY ID - CAT 2, LEV1
RXDDCI2B	DRUG CATEGORY ID - CAT 2, LEV 2
RXDDCI2C	DRUG CATEGORY ID - CAT 2, LEV 3
RXDDCI3A	DRUG CATEGORY ID - CAT 3, LEV 1
RXDDCI3B	DRUG CATEGORY ID - CAT 3, LEV 2
RXDDCI3C	DRUG CATEGORY ID - CAT 3, LEV 3
RXDDCI4A	DRUG CATEGORY ID - CAT 4, LEV 1
RXDDCI4B	DRUG CATEGORY ID - CAT 4, LEV 2
RXDDCI4C	DRUG CATEGORY ID - CAT 4, LEV 3
RXDDCN1A	DRUG CATEGORY NAME - CAT 1, LEV 1
RXDDCN1B	DRUG CATEGORY NAME - CAT 1, LEV 2
RXDDCN1C	DRUG CATEGORY NAME - CAT 1, LEV 3
RXDDCN2A	DRUG CATEGORY NAME - CAT 2, LEV 1
RXDDCN2B	DRUG CATEGORY NAME - CAT 2, LEV 2
RXDDCN2C	DRUG CATEGORY NAME - CAT 2, LEV 3
RXDDCN3A	DRUG CATEGORY NAME - CAT 3, LEV 1
RXDDCN3B	DRUG CATEGORY NAME - CAT 3, LEV 2
RXDDCN3C	DRUG CATEGORY NAME - CAT 3, LEV 3
RXDDCN4A	DRUG CATEGORY NAME - CAT 4, LEV 1
RXDDCN4B	DRUG CATEGORY NAME - CAT 4, LEV 2
RXDDCN4C	DRUG CATEGORY NAME - CAT 4, LEV 3
RXDICI1A	INGREDIENT CATEGORY ID - CAT 1, LEV 1
RXDICI1B	INGREDIENT CATEGORY ID - CAT 1, LEV 2
RXDICI1C	INGREDIENT CATEGORY ID - CAT 1, LEV 3
RXDICI2A	INGREDIENT CATEGORY ID - CAT 2, LEV 1
RXDICI2B	INGREDIENT CATEGORY ID - CAT 2, LEV 2
RXDICI2C	INGREDIENT CATEGORY ID - CAT 2, LEV 3
RXDICI3A	INGREDIENT CATEGORY ID - CAT 3, LEV 1
RXDICI3B	INGREDIENT CATEGORY ID - CAT 3, LEV 2
RXDICI3C	INGREDIENT CATEGORY ID - CAT 3, LEV 3
RXDICI4A	INGREDIENT CATEGORY ID - CAT 4, LEV 1
RXDICI4B	INGREDIENT CATEGORY ID - CAT 4, LEV 2
RXDICI4C	INGREDIENT CATEGORY ID - CAT 4, LEV 3
RXDICI5A	INGREDIENT CATEGORY ID - CAT 5, LEV 1
RXDICI5B	INGREDIENT CATEGORY ID - CAT 5, LEV 2
RXDICI5C	INGREDIENT CATEGORY ID - CAT 5, LEV 3
RXDICI6A	INGREDIENT CATEGORY ID - CAT 6, LEV 1
RXDICI6B	INGREDIENT CATEGORY ID - CAT 6, LEV 2
RXDICI6C	INGREDIENT CATEGORY ID - CAT 6, LEV 3
RXDICN1A	INGREDIENT CATEGORY NAME - CAT 1, LEV 1
RXDICN1B	INGREDIENT CATEGORY NAME - CAT 1, LEV 2
RXDICN1C	INGREDIENT CATEGORY NAME - CAT 1, LEV 3
RXDICN2A	INGREDIENT CATEGORY NAME - CAT 2, LEV 1
RXDICN2B	INGREDIENT CATEGORY NAME - CAT 2, LEV 2
RXDICN2C	INGREDIENT CATEGORY NAME - CAT 2, LEV 3
RXDICN3A	INGREDIENT CATEGORY NAME - CAT 3, LEV 1
RXDICN3B	INGREDIENT CATEGORY NAME - CAT 3, LEV 2
RXDICN3C	INGREDIENT CATEGORY NAME - CAT 3, LEV 3
RXDICN4A	INGREDIENT CATEGORY NAME - CAT 4, LEV 1
RXDICN4B	INGREDIENT CATEGORY NAME - CAT 4, LEV 2
RXDICN4C	INGREDIENT CATEGORY NAME - CAT 4, LEV 3
RXDICN5A	INGREDIENT CATEGORY NAME - CAT 5, LEV 1
RXDICN5B	INGREDIENT CATEGORY NAME - CAT 5, LEV 2
RXDICN5C	INGREDIENT CATEGORY NAME - CAT 5, LEV 3
RXDICN6A	INGREDIENT CATEGORY NAME - CAT 6, LEV 1
RXDICN6B	INGREDIENT CATEGORY NAME - CAT 6, LEV 2
RXDICN6C	INGREDIENT CATEGORY NAME - CAT 6, LEV 3

 

Analytic Notes

The variable RXDCOUNT provides a count of all prescription products reported in the RXQ adjusting for products moved into or out of the final file. The count includes products reported as “refused” or “don’t know” by participants who reported they had taken a prescription medication but did not know the name of the medication or refused to report the name of the medication. Drugs released as “unknown drug” are also included in the count. However, prescription supplements in the DSQ are not included in the total count. Therefore, this variable does not provide a comprehensive count of all prescription products used by the survey participant.

In some cases, it may appear as though participants reported the same prescription drug more than once. That is, the same generic drug name and code may be listed more than once. There are a several reason for these duplicates. Participants may have reported different brand names, which had the same generic drug name (e.g., “Glucophage” or “Glumetza” vs. “Metformin”). The medications may have been different forms or dosages of the same product (e.g., Albuterol “oral tablet” vs. “inhalation solution” or Aripiprazole “2 mg” vs. “5 mg”). Participants may have reported different lengths of use or reasons for use of the products.

The health problem as the main reason for taking medication was self-reported. The released variables, ICD-10-CM codes/description, were used to classify the health problems related to the medication use, and should not be considered as diagnoses from physicians.

During the data editing process, outlier values were examined. When there was insufficient information to conclude that values were invalid, they were left in the data set. Analysts should examine the distribution of the data and consider if it is appropriate to include or exclude extreme values in a given analysis.

Respondent sequence number (SEQN) in the prescription medication data is not a unique identifier. Participants who reported the use of multiple prescription drugs will have multiple records, that is, a record for each drug. Analysts should convert a drug-level data to a person-level data, that is, a record for each person, before merging it with NHANES demographic and other data files by using SEQN.

Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for further details on the use of sample weights and other analytic issues.

References

• In accordance with the license agreement, NCHS publications, tabulations, and software applications should cite the Multum Lexicon as the source and basis for the coding and classification of the NHANES drug data.

Codebook and Frequencies