Birth weight differences between those offered financial voucher incentives for verified smoking cessation and control participants enrolled in the Cessation in Pregnancy Incentives Trial (CPIT), employing an intuitive approach and a Complier Average Causal Effects (CACE) analysis

McConnachie, A. , Haig, C. , Sinclair, L., Bauld, L. and Tappin, D. M. (2017) Birth weight differences between those offered financial voucher incentives for verified smoking cessation and control participants enrolled in the Cessation in Pregnancy Incentives Trial (CPIT), employing an intuitive approach and a Complier Average Causal Effects (CACE) analysis. Trials, 18, 337. (doi:10.1186/s13063-017-2053-x) (PMID:28728583) (PMCID:PMC5520300)

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Abstract

Background: The Cessation in Pregnancy Incentives Trial (CPIT), which offered financial incentives for smoking cessation during pregnancy showed a clinically and statistically significant improvement in cessation. However, infant birth weight was not seen to be affected. This study re-examines birth weight using an intuitive and a complier average causal effects (CACE) method to uncover important information missed by intention-to-treat analysis. Methods: CPIT offered financial incentives up to £400 to pregnant smokers to quit. With incentives, 68 women (23.1%) were confirmed non-smokers at primary outcome, compared to 25 (8.7%) without incentives, a difference of 14.3% (Fisher test, p < 0.0001). For this analysis, randomised groups were split into three theoretical sub-groups: independent quitters - quit without incentives, hardened smokers - could not quit even with incentives and potential quitters - required the addition of financial incentives to quit. Viewed in this way, the overall birth weight gain with incentives is attributable only to potential quitters. We compared an intuitive approach to a CACE analysis. Results: Mean birth weight of potential quitters in the incentives intervention group (who therefore quit) was 3338 g compared with potential quitters in the control group (who did not quit) 3193 g. The difference attributable to incentives, was 3338 – 3193 = 145 g (95% CI −617, +803). The mean difference in birth weight between the intervention and control groups was 21 g, and the difference in the proportion who managed to quit was 14.3%. Since the intervention consisted of the offer of incentives to quit smoking, the intervention was received by all women in the intervention group. However, “compliance” was successfully quitting with incentives, and the CACE analysis yielded an identical result, causal birth weight increase 21 g ÷ 0.143 = 145 g. Conclusions: Policy makers have great difficulty giving pregnant women money to stop smoking. This study indicates that a small clinically insignificant improvement in average birth weight is likely to hide an important clinically significant increase in infants born to pregnant smokers who want to stop but cannot achieve smoking cessation without the addition of financial voucher incentives.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Tappin, Professor David and McConnachie, Dr Alex and Sinclair, Ms Lesley and Haig, Dr Caroline
Authors: McConnachie, A., Haig, C., Sinclair, L., Bauld, L., and Tappin, D. M.
College/School:College of Medical Veterinary and Life Sciences > Institute of Health and Wellbeing > MRC/CSO Unit
College of Medical Veterinary and Life Sciences > Institute of Health and Wellbeing > Robertson Centre
College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing
Journal Name:Trials
Publisher:BioMed Central
ISSN:1745-6215
ISSN (Online):1745-6215
Copyright Holders:Copyright © 2017 The Authors
First Published:First published in Trials 18:337
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
497301Financial Incentives For Smoking Cessation In Pregnancy: A Phase II Randomised Controlled TrialDavid TappinScottish Executive Health Department (SEHHD-CSO)CZH/4/594MVLS SM - CHILD HEALTH