Metric Facts
Weight gain from quitting smoking · provisional
Headline
kg more weight gain from quitting, averaged over everyone in the study+3.44
kg more weight gain from quitting, averaged over everyone in the study+3.44
Plausible range +2.41 to +4.47 · Robust (sandwich) variance, as from a generalized estimating equations fit with independence
We followed 1,566 adult smokers from a health check in 1971–75 to a second visit in 1982. We compare weight change in people who quit with people who did not, after reweighting so the two groups match on nine traits.
CountedPeople who: adults aged 25–74 who smoked at the first health check and had the basic facts recorded (sex, age, race, weight, height, education, alcohol use, smoking intensity); had their weight measured at the 1982 visit. n = 1,566
Clock startsEach person's first health check, held some time between 1971 and 1975.
Time to quitFrom 1 to 73 months (up to, not including, 73) (exposure). Any time between the first health check and the 1982 visit. Quitting counts if the person reported having quit by 1982.
1982 visitFrom 73 to 144 months (up to, not including, 144) (observation). The second visit in 1982, roughly 7 to 11 years after the first, depending on when that was.
What countsBody weight at the 1982 visit minus body weight at the first health check, in kilograms.
Combined asAverage weight change in each group, with each person counted according to their weight.
Compared byCompare the two reweighted groups. Because both are made to resemble the whole study, the gap estimates what quitting would do on average across all of these smokers.
mean if all quit − mean if none quit · ATEAdjusted forsex, race, age (linear and squared), education (5 levels), cigarettes per day (linear and squared), years smoking (linear and squared), exercise (3 levels), how active day to day (3 levels), baseline weight (linear and squared)
Kind of claimPoints toward a cause, with assumptions. The design removes some alternative explanations, not all. Read it as a cause only if its assumptions hold.
CompletenessThe card does not state when the data were complete, so we cannot confirm every window was fully observed.
Before you repeat it
This is only causal if the nine traits capture everything that made people both quit and gain weight. The study also kept only people alive and measured in 1982, which the authors flag as a possible source of bias they chose not to fix.
Caveats
- ↕Only as good as the nine traits
- ↕Survivors only
- ◎Quitting happened at different times
- ◎The interval is wider than it needs to be
Don't say
- Quitters gained 3.4 kg.
- This is the effect for people who actually quit.
- The raw gap of 2.5 kg is the effect of quitting.
4 known gap(s) between description and code: Who is in the study; Treatment model in the censoring analysis; Input file; Year labels.
↑ may overstate · ↓ may understate · ± uncertainty understated · ↕ either way · ◎ limits scope. Owner: data-visual-explainer worked example (public data). Updated 2026-10-07. Data as of Hernán & Robins, What If (version of 19 Aug 2026); recomputed 2026-10-07. Sources: S1 hernanrobins_WhatIf_19aug26.pdf, S2 chapter12.R, S3 nhefs.csv, S4 analysis.py, S5 chapter15.R.