Does smoking cessation result in improved mental health? A comparison of regression modelling and propensity score matching.
OBJECTIVE
Smokers report that smoking is therapeutic; a recent meta-analysis suggests the contrary. However, the association in that review may be explained by group-membership bias and confounding. Propensity score matching (PSM) aims to produce causal estimates from observational data. We examined the association between cessation and change in mental health before and after PSM.


METHODS
A secondary analysis of prospective data from 5 placebo-controlled randomised trials for smoking reduction.


METHODS
All participants were adult smokers and had smoked for at least 3 years. Participants were excluded if they were pregnant, breast feeding, under psychiatric care, deemed to be unfit by a general practitioner or part of a cessation programme. In total, 937 participants provided smoking data at both 6-month and 12-month follow-ups. Of these, 68 were confirmed as abstinent at both 6 and 12 months and 589 as continuous smokers at both follow-ups.


METHODS
Change in mental health (36-item Short Form Survey (SF-36), scored 0-100) from baseline (while all participants were smokers) to 12-month follow-up (after cessation) was compared between quitters and continuing smokers with and without adjustment, and after PSM.


RESULTS
Before matching, quitters' mental health scores improved compared with continuing smokers', the mean difference and 95% CI was 5.5 (1.6 to 9.4). After adjustment, the difference was 4.5 (0.6 to 8.5), and after PSM, the difference was 3.4 (-2.2 to 8.9).


CONCLUSIONS
Improvements in mental health after smoking cessation may be partly but not completely explained by group membership bias and confounding.
School of Health & Population Sciences, University of Birmingham, Birmingham, UK UK Centre for Tobacco and Alcohol Studies, Birmingham, UK.
Gemma
G
Taylor
School of Health & Population Sciences, University of Birmingham, Birmingham, UK.
Alan
A
Girling
UK Centre for Tobacco and Alcohol Studies, Birmingham, UK Institute of Psychiatry, King's College London, London, UK.
Ann
A
McNeill
UK Centre for Tobacco and Alcohol Studies, Birmingham, UK Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, UK.
Paul
P
Aveyard
D000328:Adult; D015982:Bias; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008603:Mental Health / Q000706:statistics & numerical data*; D008875:Middle Aged; D057216:Propensity Score; D011446:Prospective Studies; D012907:Smoking / Q000523:psychology*; D016540:Smoking Cessation / Q000523:psychology*; D011795:Surveys and Questionnaires
EPIDEMIOLOGY; MENTAL HEALTH; PRIMARY CARE; PUBLIC HEALTH; SMOKING AND TOBACCO