# NHANES variable map — the reproduction's own crosswalk

*Generated by `R/07_variable_map.R` from the files in `data/raw/`. Do not edit by hand.*
*Cycle availability, labels and missing-value conventions below were read out of the
.xpt files, not copied from documentation.*

Every variable this reproduction touches, and for each one the four things students
most often get wrong:

1. **Where it lives** — which component file, and therefore which download
2. **What its raw codes mean** — and whether a `77`-looking value is a code or a measurement
3. **Whether it exists in every cycle** — several do not
4. **What we did to it** — the line in our pipeline that reads or transforms it

> **This page is a method, not just an answer.** When you meet an unfamiliar NHANES
> variable in *your own* paper, these are the questions to ask of it, in this order.
> The loop runs: paper sentence → operational concept → NHANES variable
> → component → **that cycle's** codebook → raw `.xpt` → your
> implementation → cohort consequence.

Three different kinds of link, which are easy to conflate:

| Link | Goes to | Use it when |
|---|---|---|
| **codebook** | the CDC documentation page, anchored at that variable | you need the official definition, the value labels, or the frequencies |
| **.xpt** | the raw data file for that cycle | you are downloading it yourself |
| **our code** | the line in this pipeline that reads or derives it | you want to see what *we* did, and disagree with it |

Cycle letters: **E** 2007-08 · **F** 2009-10 · **G** 2011-12 · **H** 2013-14 ·
**I** 2015-16 · **J** 2017-18. The *file* name carries the suffix (`BMX_H.xpt`);
the *variable* name inside usually does not (`BMXBMI` in every cycle).

---

## Join key

| Concept | Variable | Component | Cycles | Label (from the file) | Missing convention | Links |
|---|---|---|---|---|---|---|
| Respondent ID | `SEQN` | `DEMO` | all six | Respondent sequence number | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.htm#SEQN) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.xpt) · `R/02_build_analytic.R:48` |

## Eligibility

| Concept | Variable | Component | Cycles | Label (from the file) | Missing convention | Links |
|---|---|---|---|---|---|---|
| Age | `RIDAGEYR` | `DEMO` | all six | Age at Screening Adjudicated - Recode | `NA` only — `7`, `9`, `77` are real values (n=1282, 1258, 300): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.htm#RIDAGEYR) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.xpt) · `R/02_build_analytic.R:56` |

## Survey design

| Concept | Variable | Component | Cycles | Label (from the file) | Missing convention | Links |
|---|---|---|---|---|---|---|
| MEC weight | `WTMEC2YR` | `DEMO` | all six | Full Sample 2 Year MEC Exam Weight | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.htm#WTMEC2YR) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.xpt) · `R/02_build_analytic.R:57` |
| Interview weight | `WTINT2YR` | `DEMO` | all six | Full Sample 2 Year Interview Weight | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.htm#WTINT2YR) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.xpt) · `R/02_build_analytic.R:57` |
| Cycle indicator | `SDDSRVYR` | `DEMO` | all six | Data Release Number | `NA` only — `7`, `9` are real values (n=9756, 9971): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.htm#SDDSRVYR) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.xpt) · `R/02_build_analytic.R:57` |
| Fasting subsample weight | `WTSAF2YR` | `TRIGLY` | all six | Fasting Subsample 2 Year MEC Weight ⚠ | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/TRIGLY_E.htm#WTSAF2YR) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/TRIGLY_E.xpt) · `R/02_build_analytic.R:61` |
| Stratum | `SDMVSTRA` | `DEMO` | all six | Masked Variance Pseudo-Stratum | `NA` only — `77`, `99` are real values (n=823, 682): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.htm#SDMVSTRA) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.xpt) · `R/02_build_analytic.R:57` |
| PSU | `SDMVPSU` | `DEMO` | all six | Masked Variance Pseudo-PSU | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.htm#SDMVPSU) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.xpt) · `R/02_build_analytic.R:57` |

> ⚠ **`WTSAF2YR`** — A **design** variable living in a laboratory file. Build the survey design on the full frame, then `subset()` - never on the subsample alone.

## Case definition (FLI)

| Concept | Variable | Component | Cycles | Label (from the file) | Missing convention | Links |
|---|---|---|---|---|---|---|
| Triglycerides | `LBXTR` | `TRIGLY` | all six | Triglyceride (mg/dL) | `NA` only — `77`, `99` are real values (n=152, 117): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/TRIGLY_E.htm#LBXTR) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/TRIGLY_E.xpt) · `R/00_setup.R:52` |
| BMI | `BMXBMI` | `BMX` | all six | Body Mass Index (kg/m**2) | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BMX_E.htm#BMXBMI) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BMX_E.xpt) · `R/02_build_analytic.R:58` |
| GGT | `LBXSGTSI` | `BIOPRO` | all six | Gamma glutamyl transferase (U/L) | `NA` only — `7`, `9`, `77`, `99` are real values (n=519, 1228, 27, 14): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BIOPRO_E.htm#LBXSGTSI) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BIOPRO_E.xpt) · `R/00_setup.R:53` |
| Waist circumference | `BMXWAIST` | `BMX` | all six | Waist Circumference (cm) | `NA` only — `77`, `99` are real values (n=119, 132): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BMX_E.htm#BMXWAIST) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BMX_E.xpt) · `R/02_build_analytic.R:58` |

## Cardiometabolic 1 (adiposity)

| Concept | Variable | Component | Cycles | Label (from the file) | Missing convention | Links |
|---|---|---|---|---|---|---|
| BMI | `BMXBMI` | `BMX` | all six | Body Mass Index (kg/m**2) | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BMX_E.htm#BMXBMI) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BMX_E.xpt) · `R/02_build_analytic.R:58` |
| Waist circumference | `BMXWAIST` | `BMX` | all six | Waist Circumference (cm) | `NA` only — `77`, `99` are real values (n=119, 132): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BMX_E.htm#BMXWAIST) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BMX_E.xpt) · `R/02_build_analytic.R:58` |

## Cardiometabolic 2 (glycaemia)

| Concept | Variable | Component | Cycles | Label (from the file) | Missing convention | Links |
|---|---|---|---|---|---|---|
| Fasting glucose | `LBXGLU` | `GLU` | all six | Fasting Glucose (mg/dL) | `NA` only — `77`, `99` are real values (n=50, 709): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/GLU_E.htm#LBXGLU) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/GLU_E.xpt) · `R/00_setup.R:55` |
| HbA1c | `LBXGH` | `GHB` | all six | Glycohemoglobin (%) | `NA` only — `7`, `9` are real values (n=173, 26): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/GHB_E.htm#LBXGH) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/GHB_E.xpt) · `R/00_setup.R:54` |
| Diabetes diagnosis | `DIQ010` | `DIQ` | all six | Doctor told you have diabetes | **reserved `7`, `9`** (n=3, 32) — strip before any rule | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DIQ_E.htm#DIQ010) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DIQ_E.xpt) · `R/02_build_analytic.R:70` |
| Insulin | `DIQ050` | `DIQ` | all six | Taking insulin now | **reserved `7`, `9`** (n=4, 5) — strip before any rule | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DIQ_E.htm#DIQ050) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DIQ_E.xpt) · `R/02_build_analytic.R:70` |
| Oral hypoglycaemics | `DIQ070` | `DIQ` | **FGHIJ only** | Take diabetic pills to lower blood sugar | **reserved `7`, `9`** (n=1, 10) — strip before any rule | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2009/DataFiles/DIQ_F.htm#DIQ070) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2009/DataFiles/DIQ_F.xpt) · `R/02_build_analytic.R:70` |

## Cardiometabolic 3 (blood pressure)

| Concept | Variable | Component | Cycles | Label (from the file) | Missing convention | Links |
|---|---|---|---|---|---|---|
| Systolic (reading 1 of 4) | `BPXSY1` | `BPX` | all six | Systolic:  Blood pres (1st rdg) mm Hg | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BPX_E.htm#BPXSY1) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BPX_E.xpt) · `R/02_build_analytic.R:59` |
| Diastolic (reading 1 of 4) | `BPXDI1` | `BPX` | all six | Diastolic:  Blood pres (1st rdg) mm Hg ⚠ | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BPX_E.htm#BPXDI1) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BPX_E.xpt) · `R/02_build_analytic.R:60` |
| On BP medication | `BPQ050A` | `BPQ` | all six | Now taking prescribed medicine for HBP | **reserved `9`** (n=3) — strip before any rule | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BPQ_E.htm#BPQ050A) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BPQ_E.xpt) · `R/02_build_analytic.R:69` |

> ⚠ **`BPXDI1`** — A diastolic reading of **0 is a measurement**. NHANES records a failure to obtain a reading as `NA`, separately. Do not `na_if(., 0)`.

## Cardiometabolic 4 (triglycerides)

| Concept | Variable | Component | Cycles | Label (from the file) | Missing convention | Links |
|---|---|---|---|---|---|---|
| Triglycerides | `LBXTR` | `TRIGLY` | all six | Triglyceride (mg/dL) | `NA` only — `77`, `99` are real values (n=152, 117): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/TRIGLY_E.htm#LBXTR) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/TRIGLY_E.xpt) · `R/00_setup.R:52` |
| On lipid medication | `BPQ100D` | `BPQ` | all six | Now taking prescribed medicine | **reserved `9`** (n=14) — strip before any rule | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BPQ_E.htm#BPQ100D) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BPQ_E.xpt) · `R/02_build_analytic.R:69` |

## Cardiometabolic 5 (HDL)

| Concept | Variable | Component | Cycles | Label (from the file) | Missing convention | Links |
|---|---|---|---|---|---|---|
| HDL cholesterol | `LBDHDD` | `HDL` | all six | Direct HDL-Cholesterol (mg/dL) | `NA` only — `7`, `77`, `99` are real values (n=1, 255, 32): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/HDL_E.htm#LBDHDD) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/HDL_E.xpt) · `R/00_setup.R:56` |

## Exposure

| Concept | Variable | Component | Cycles | Label (from the file) | Missing convention | Links |
|---|---|---|---|---|---|---|
| Height (for WHtR) | `BMXHT` | `BMX` | all six | Standing Height (cm) | `NA` only — `99` is a real value (n=16): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BMX_E.htm#BMXHT) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BMX_E.xpt) · `R/02_build_analytic.R:58` |
| Race/ethnicity (Asian BMI cut) | `RIDRETH3` | `DEMO` | **GHIJ only** | Race/Hispanic origin w/ NH Asian ⚠ | `NA` only — `7` is a real value (n=1996): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2011/DataFiles/DEMO_G.htm#RIDRETH3) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2011/DataFiles/DEMO_G.xpt) · `R/02_build_analytic.R:56` |

> ⚠ **`RIDRETH3`** — This is what identifies Asian participants for the paper's lower BMI threshold - so the rule cannot be applied in 2007-2010 at all.

## Alcohol exclusion

| Concept | Variable | Component | Cycles | Label (from the file) | Missing convention | Links |
|---|---|---|---|---|---|---|
| Drinks per drinking day | `ALQ130` | `ALQ` | all six | Avg # alcoholic drinks/day -past 12 mos ⚠ | **reserved `777`, `999`** (n=3, 28) — strip before any rule, but `7`, `9` are real values (n=197, 47): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALQ_E.htm#ALQ130) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALQ_E.xpt) · `R/02_build_analytic.R:67` |
| Drinking frequency (quantity) | `ALQ120Q` | `ALQ` | **EFGHI only** | How often drink alcohol over past 12 mos | **reserved `777`, `999`** (n=2, 25) — strip before any rule, but `7`, `9` are real values (n=1146, 17): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALQ_E.htm#ALQ120Q) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALQ_E.xpt) · `R/02_build_analytic.R:67` |
| Drinking frequency (unit) | `ALQ120U` | `ALQ` | **EFGHI only** | # days drink alcohol per wk, mo, yr | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALQ_E.htm#ALQ120U) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALQ_E.xpt) · `R/02_build_analytic.R:67` |
| Drinking frequency (2017-18 redesign) | `ALQ121` | `ALQ` | **J only** | Past 12 mo how often have alcohol drink ⚠ | **reserved `77`, `99`** (n=2, 2) — strip before any rule, but `7`, `9` are real values (n=351, 476): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/ALQ_J.htm#ALQ121) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/ALQ_J.xpt) · `R/02_build_analytic.R:67` |

> ⚠ **`ALQ130`** — CDC's **SAS Label** reads *"Avg # alcohol drinks/day - past 12 mos"*. CDC's **English Text** for the same variable reads *"During the past 12 months, on those days that {you} drank alcoholic beverages, on the average, how many drinks did {you} have?"* — that is drinks per *drinking* day. Applying a per-day threshold to it directly over-excludes ~2,000 people here; average intake needs frequency x quantity. **The short label is not the question.** Read the English Text, every time.

> ⚠ **`ALQ121`** — Its reserved codes are **`77` (Refused) and `99` (Don't know)**, not the `777`/`999` used by `ALQ130` — a rule hard-coded to `c(777, 999)` misses them. And `7` and `9` are ordinary answers here: **7 = "Once a month"**, **9 = "3 to 6 times in the last year"**. CDC's own Analytic Notes state *"ALQ120Q and ALQ120U became ALQ121"* in 2017-18, so this is an instrument change, not a missing column.

## Covariate

| Concept | Variable | Component | Cycles | Label (from the file) | Missing convention | Links |
|---|---|---|---|---|---|---|
| Sex | `RIAGENDR` | `DEMO` | all six | Gender | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.htm#RIAGENDR) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.xpt) · `R/02_build_analytic.R:56` |
| Race/ethnicity (all cycles) | `RIDRETH1` | `DEMO` | all six | Race/Ethnicity - Recode | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.htm#RIDRETH1) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.xpt) · `R/02_build_analytic.R:56` |
| Income-to-poverty ratio | `INDFMPIR` | `DEMO` | all six | Ratio of family income to poverty | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.htm#INDFMPIR) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DEMO_E.xpt) · `R/02_build_analytic.R:57` |
| Ever smoked 100 cigarettes | `SMQ020` | `SMQ` | all six | Smoked at least 100 cigarettes in life | **reserved `7`, `9`** (n=6, 19) — strip before any rule | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/SMQ_E.htm#SMQ020) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/SMQ_E.xpt) · `R/02_build_analytic.R:68` |
| Current smoking | `SMQ040` | `SMQ` | all six | Do you now smoke cigarettes | **reserved `7`** (n=3) — strip before any rule | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/SMQ_E.htm#SMQ040) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/SMQ_E.xpt) · `R/02_build_analytic.R:68` |
| Coronary heart disease | `MCQ160C` | `MCQ` | all six | Ever told you had coronary heart disease | **reserved `7`, `9`** (n=2, 136) — strip before any rule | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/MCQ_E.htm#MCQ160C) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/MCQ_E.xpt) · `R/02_build_analytic.R:71` |
| Heart failure | `MCQ160B` | `MCQ` | all six | Ever told had congestive heart failure | **reserved `7`, `9`** (n=1, 94) — strip before any rule | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/MCQ_E.htm#MCQ160B) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/MCQ_E.xpt) · `R/02_build_analytic.R:71` |
| Stroke | `MCQ160F` | `MCQ` | all six | Ever told you had a stroke | **reserved `7`, `9`** (n=1, 49) — strip before any rule | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/MCQ_E.htm#MCQ160F) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/MCQ_E.xpt) · `R/02_build_analytic.R:71` |
| Cancer | `MCQ220` | `MCQ` | all six | Ever told you had cancer or malignancy | **reserved `7`, `9`** (n=1, 29) — strip before any rule | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/MCQ_E.htm#MCQ220) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/MCQ_E.xpt) · `R/02_build_analytic.R:72` |
| Weak/failing kidneys | `KIQ022` | `KIQ_U` | all six | Ever told you had weak/failing kidneys | **reserved `7`, `9`** (n=1, 53) — strip before any rule | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/KIQ_U_E.htm#KIQ022) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/KIQ_U_E.xpt) · `R/02_build_analytic.R:73` |
| Serum creatinine | `LBXSCR` | `BIOPRO` | all six | Creatinine (mg/dL) | `NA` only | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BIOPRO_E.htm#LBXSCR) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/BIOPRO_E.xpt) · `R/00_setup.R:53` |
| Urine albumin | `URXUMA` | `ALB_CR` | all six | Albumin, urine (ug/mL) | `NA` only — `7`, `9`, `77`, `99` are real values (n=302, 254, 4, 11): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALB_CR_E.htm#URXUMA) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALB_CR_E.xpt) · `R/02_build_analytic.R:74` |
| Urine creatinine | `URXUCR` | `ALB_CR` | all six | Creatinine, urine (mg/dL) | `NA` only — `7`, `9`, `77`, `99` are real values (n=22, 50, 252, 228): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALB_CR_E.htm#URXUCR) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALB_CR_E.xpt) · `R/02_build_analytic.R:74` |
| Albumin-creatinine ratio | `URDACT` | `ALB_CR` | **FGHIJ only** | First albumin creatinine ratio (mg/g) | `NA` only — `7`, `9` are real values (n=44, 31): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2009/DataFiles/ALB_CR_F.htm#URDACT) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2009/DataFiles/ALB_CR_F.xpt) · `R/02_build_analytic.R:74` |
| Sedentary minutes | `PAD680` | `PAQ` | all six | Minutes sedentary activity | **reserved `7777`, `9999`** (n=5, 187) — strip before any rule, but `7`, `9` are real values (n=7, 1): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/PAQ_E.htm#PAD680) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/PAQ_E.xpt) · `R/02_build_analytic.R:75` |
| Total cholesterol | `LBXTC` | `TCHOL` | all six | Total Cholesterol (mg/dL) | `NA` only — `77`, `99` are real values (n=1, 23): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/TCHOL_E.htm#LBXTC) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/TCHOL_E.xpt) · `R/00_setup.R:57` |
| LDL cholesterol | `LBDLDL` | `TRIGLY` | all six | LDL-cholesterol (mg/dL) | `NA` only — `9`, `77`, `99` are real values (n=1, 142, 197): do **not** strip | [codebook](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/TRIGLY_E.htm#LBDLDL) · [.xpt](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/TRIGLY_E.xpt) · `R/02_build_analytic.R:61` |

---

## Not every variable exists in every cycle

Verified against the files, not assumed. `bind_rows()` will happily fill an absent
column with `NA` for a third of your sample, and that is **a changing instrument, not
**Which cycle's codebook are you reading?** For these variables that is not a
rhetorical question, so every applicable cycle is linked separately.

| Variable | Component | Present in | **Absent in** | Codebook, by cycle |
|---|---|---|---|---|
| `DIQ070` | `DIQ` | FGHIJ | **E** | [F](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2009/DataFiles/DIQ_F.htm) · [G](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2011/DataFiles/DIQ_G.htm) · [H](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2013/DataFiles/DIQ_H.htm) · [I](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2015/DataFiles/DIQ_I.htm) · [J](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/DIQ_J.htm) |
| `RIDRETH3` | `DEMO` | GHIJ | **EF** | [G](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2011/DataFiles/DEMO_G.htm) · [H](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2013/DataFiles/DEMO_H.htm) · [I](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2015/DataFiles/DEMO_I.htm) · [J](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/DEMO_J.htm) |
| `ALQ120Q` | `ALQ` | EFGHI | **J** | [E](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALQ_E.htm) · [F](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2009/DataFiles/ALQ_F.htm) · [G](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2011/DataFiles/ALQ_G.htm) · [H](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2013/DataFiles/ALQ_H.htm) · [I](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2015/DataFiles/ALQ_I.htm) |
| `ALQ120U` | `ALQ` | EFGHI | **J** | [E](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALQ_E.htm) · [F](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2009/DataFiles/ALQ_F.htm) · [G](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2011/DataFiles/ALQ_G.htm) · [H](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2013/DataFiles/ALQ_H.htm) · [I](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2015/DataFiles/ALQ_I.htm) |
| `ALQ121` | `ALQ` | J | **EFGHI** | [J](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/ALQ_J.htm) |
| `URDACT` | `ALB_CR` | FGHIJ | **E** | [F](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2009/DataFiles/ALB_CR_F.htm) · [G](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2011/DataFiles/ALB_CR_G.htm) · [H](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2013/DataFiles/ALB_CR_H.htm) · [I](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2015/DataFiles/ALB_CR_I.htm) · [J](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/ALB_CR_J.htm) |
| `ALQ130` | `ALQ` | all six | *none — but the instrument around it changed in J* | [E](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/ALQ_E.htm) · [F](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2009/DataFiles/ALQ_F.htm) · [G](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2011/DataFiles/ALQ_G.htm) · [H](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2013/DataFiles/ALQ_H.htm) · [I](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2015/DataFiles/ALQ_I.htm) · [J](https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/ALQ_J.htm) |

## Reserved codes are not a property of NHANES. They are a property of the variable.

The single most dangerous piece of half-learned NHANES advice is *"strip 777 and 999"*.
Applied to a laboratory variable it deletes real measurements. Below, every
sentinel-looking value this reproduction's variables actually contain, classified by
whether it sits outside the variable's own legitimate range.

| Variable | Reserved codes | Sentinel-looking values that are **real** | Largest legitimate value |
|---|---|---|---|
| `RIDAGEYR` | none | `7`, `9`, `77` (n=1282, 1258, 300) | 80 |
| `SDDSRVYR` | none | `7`, `9` (n=9756, 9971) | 10 |
| `SDMVSTRA` | none | `77`, `99` (n=823, 682) | 148 |
| `LBXTR` | none | `77`, `99` (n=152, 117) | 4,233 |
| `LBXSGTSI` | none | `7`, `9`, `77`, `99` (n=519, 1228, 27, 14) | 1,510 |
| `BMXWAIST` | none | `77`, `99` (n=119, 132) | 179 |
| `LBXGLU` | none | `77`, `99` (n=50, 709) | 584 |
| `LBXGH` | none | `7`, `9` (n=173, 26) | 17.8 |
| `DIQ010` | `7`, `9` | — | 3 |
| `DIQ050` | `7`, `9` | — | 2 |
| `DIQ070` | `7`, `9` | — | 2 |
| `BPQ050A` | `9` | — | 2 |
| `BPQ100D` | `9` | — | 2 |
| `LBDHDD` | none | `7`, `77`, `99` (n=1, 255, 32) | 226 |
| `BMXHT` | none | `99` (n=16) | 204.5 |
| `RIDRETH3` | none | `7` (n=1996) | 6 |
| `ALQ130` | `777`, `999` | `7`, `9` (n=197, 47) | 83 |
| `ALQ120Q` | `777`, `999` | `7`, `9` (n=1146, 17) | 365 |
| `ALQ121` | `77`, `99` | `7`, `9` (n=351, 476) | 10 |
| `SMQ020` | `7`, `9` | — | 2 |
| `SMQ040` | `7` | — | 3 |
| `MCQ160C` | `7`, `9` | — | 2 |
| `MCQ160B` | `7`, `9` | — | 2 |
| `MCQ160F` | `7`, `9` | — | 2 |
| `MCQ220` | `7`, `9` | — | 2 |
| `KIQ022` | `7`, `9` | — | 2 |
| `URXUMA` | none | `7`, `9`, `77`, `99` (n=302, 254, 4, 11) | 24,440 |
| `URXUCR` | none | `7`, `9`, `77`, `99` (n=22, 50, 252, 228) | 800 |
| `URDACT` | none | `7`, `9` (n=44, 31) | 92,500 |
| `PAD680` | `7777`, `9999` | `7`, `9` (n=7, 1) | 1,380 |
| `LBXTC` | none | `77`, `99` (n=1, 23) | 813 |
| `LBDLDL` | none | `9`, `77`, `99` (n=1, 142, 197) | 375 |

> **What this table does and does not license.** For the variables used in this
> reproduction, the laboratory and examination measurements shown above use `NA` for
> missing, while several questionnaire variables use variable-specific reserved
> codes. **Do not generalise either pattern to another variable** — including
> another variable in the same component, or the same variable in another cycle.
> Check its codebook.
>
> A `77` in `LBXTR` is a triglyceride of 77 mg/dL. A `77` in `ALQ121` is a refusal.
> Same digits, opposite meaning. The point of this table is not a replacement rule
> to memorise; it is that **there is no such rule**, and the codebook decides.


## The outcome does not live in NHANES

| Concept | Variable | Source | Notes |
|---|---|---|---|
| Vital status | `MORTSTAT` | NCHS Linked Mortality File | separate fixed-width file, not an `.xpt` |
| Person-months from exam | `PERMTH_EXM` | NCHS Linked Mortality File | the clock for time-to-event |
| Linkage eligibility | `ELIGSTAT` | NCHS Linked Mortality File | not everyone is eligible for linkage |

Downloaded by `R/01_download.R` from
<https://ftp.cdc.gov/pub/Health_Statistics/NCHS/datalinkage/linked_mortality>.
Follow-up ends **31 December 2019**, per the NCHS 2019 linkage methodology document —
not inferred from the filename.


---

*Regenerate with `Rscript R/07_variable_map.R`. Codebook links use the current CDC
path `.../Public/<year>/DataFiles/<COMP>_<suffix>.htm#<VARIABLE>`; the older
`wwwn.cdc.gov/Nchs/Nhanes/<cycle>/` form no longer resolves.*