JNCI J Natl Cancer Inst (2018) 110(10): djy026 doi: 10.1093/jnci/djy026 John P. Pierce, Eric C. Leas, Tarik Benmarhnia, David R. Strong See the Notes section for the full list of authors’ afﬁliations. Correspondence to: John P. Pierce, PhD, Department of Family Medicine and Public Health, Moores UC San Diego Cancer Center, University of California, San Diego, La Jolla, CA 92093-0901 (e-mail: email@example.com). In the early 1990s, a series of randomized trials demonstrated criteria for the smoking cessation trials would rule out more the efficacy of both pharmaceutical aids with behavioral ther- than half of the smokers in the US population (4), which in itself apy for smoking cessation and treatments for metastatic breast is sufficient to question the generalizability of trial conclusions. cancer. These treatments were approved by the US Food and We agree with Imai et al. (5) that avoiding confounding is im- portant in both experimental and observational studies. They Drug Administration and quickly disseminated into clinical practice. A decade later, the population mean survival following go on to note that many current proponents of one study design a metastatic breast cancer diagnosis had improved 50%, demon- over another often misunderstand how the other method can strating the effectiveness of the treatment (1); however, there provide evidence for causal inference. Our results suggest a problem with how interventions from cessation trials have was no improvement in the proportion of smokers who had successfully quit (2). A critical public health question is how to been disseminated to the population. There is an urgent need to account for the apparent lack of translation of quitting success revisit how we help people quit smoking (6). into the population. In our study, smokers who reported using a pharmaceutical aid in their recent quit attempt rarely paired this with behav- ioral therapy. Indeed, the high quality of behavioral therapy Notes used in well-designed efficacy trials is not generally accessible Affiliations of authors: Department of Family Medicine and in the community and thus challenges the scalability of the Public Health and Moores Cancer Center, University of combined efficacious interventions. Using established propen- California, San Diego, La Jolla, CA (JPP, ECL, TB, DRS); Stanford sity score matching methods, we chose comparison groups who Prevention Research Center, Stanford University School of did or did not use a cessation aid that were matched on baseline Medicine, Palo Alto, CA (ECL); Climate, Atmospheric Science and characteristics that might confound an assessment of success- Physical Oceanography, Scripps Institution of Oceanography, La ful quitting. We achieved close matching on numerous con- Jolla, CA (TB). founders, which led to precise results indicating a null effect that was robust to several sensitivity analyses. In their correspondence, Shiffman and Gitchell are concerned References that our results could be confounded because of biases associated 1. Chia SK, Speers CH, D’Yachkova Y, et al. The impact of new chemotherapeutic with an observational study. They note that use of propensity and hormone agents on survival in a population-based cohort of women with metastatic breast cancer. Cancer. 2007;110(5):973–979. score matching was a “heroic” attempt to balance potential con- 2. Zhu S, Lee M, Zhuang Y, Gamst A, Wolfson T. Interventions to increase smok- founders in our study. But they are not sure about so-called ing cessation at the population level: How much progress has been made in “confounding by indication.” Yet we obtain good balance on self- the last two decades? Tob Control. 2012;21(2):110–118. 3. Tindle HA, Greevy RA. Smoking cessation pharmacotherapy, even without efficacy and smoking intensity, two variables associated with counseling, remains a cornerstone of treatment. J Natl Cancer Inst. 2018;110(6): both use of a pharmaceutical aid and success. Further, they worry djx246. about unmeasured/residual confounding. We note that in order 4. Motschman CA, Gass JC, Wray JM, et al. Selection criteria limit generalizability of smoking pharmacotherapy studies differentially across clinical trials and for a yet-to-be-identified variable to counteract a twofold higher laboratory studies: A systematic review on varenicline. Drug Alcohol Depend. quitting success from use of a pharmaceutical aid, it would need 2016;169:180–189. to have a substantial negative impact on quitting. If such a vari- 5. Imai K, King G, Stuart E. Misunderstandings among experimentalists and observationalists about causal inference. J Royal Stat Soc. 2008;171(part 2): able exists, let’s hope someone identifies it soon. 481–502. They appear to believe, along with others (3), that good evi- 6. Pierce JP, Cummins SE, White MM, Humphrey A, Messer K. Quitlines and nico- dence from multiple efficacy trials is all that is needed to make tine replacement for smoking cessation: Do we need to change policy? Annu causal inferences on population effectiveness. Yet, eligibility Rev Public Health. 2012;33:341–356. Received: January 19, 2018; Accepted: January 31, 2018 © The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: firstname.lastname@example.org. Downloaded from https://academic.oup.com/jnci/advance-article-abstract/doi/10.1093/jnci/djy026/4915403 by Ed 'DeepDyve' Gillespie user on 11 July 2018 CORRESPONDENCE
JNCI: Journal of the National Cancer Institute – Oxford University Press
Published: Feb 28, 2018
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