Influence of design characteristics on the outcome of retrospective cohort studies

Tobacco papers and tobacco industry ties in regulatory toxicology and pharmacology

We examined the relationship between the tobacco industry and the journal Regulatory Toxicology and Pharmacology (RTP) using the Truth Tobacco Industry Documents Library and internet sources. We determined the funding relationships, and categorised the conclusions of all 52 RTP papers on tobacco or nicotine between January 2013 and June 2015, as "positive", "negative" or "neutral" for the tobacco industry. RTP's editor, 57% (4/7) of associate editors and 37% (14/38) of editorial board members had worked or consulted for tobacco companies. Almost all (96%, 50/52) of the papers had authors with tobacco industry ties. Seventy-six percent (38/50) of these papers drew conclusions positive for industry; none drew negative conclusions. The two papers by authors not related to the tobacco industry reached conclusions negative to the industry (p < .001). These results call into question the confidence that members of the scientific community and tobacco product regulators worldwide can have in the conclusions of papers published in RTP.

Quantifying and Adjusting for Disease Misclassification Due to Loss to Follow-Up in Historical Cohort Mortality Studies

The purpose of this analysis was to quantify and adjust for disease misclassification from loss to follow-up in a historical cohort mortality study of workers where exposure was categorized as a multi-level variable. Disease classification parameters were defined using 2008 mortality data for the New Zealand population and the proportions of known deaths observed for the cohort. The probability distributions for each classification parameter were constructed to account for potential differences in mortality due to exposure status, gender, and ethnicity. Probabilistic uncertainty analysis (bias analysis), which uses Monte Carlo techniques, was then used to sample each parameter distribution 50,000 times, calculating adjusted odds ratios (ORDM-LTF) that compared the mortality of workers with the highest cumulative exposure to those that were considered never-exposed. The geometric mean ORDM-LTF ranged between 1.65 (certainty interval (CI): 0.50-3.88) and 3.33 (CI: 1.21-10.48), and the geometric mean of the disease-misclassification error factor (εDM-LTF), which is the ratio of the observed odds ratio to the adjusted odds ratio, had a range of 0.91 (CI: 0.29-2.52) to 1.85 (CI: 0.78-6.07). Only when workers in the highest exposure category were more likely than those never-exposed to be misclassified as non-cases did the ORDM-LTF frequency distributions shift further away from the null. The application of uncertainty analysis to historical cohort mortality studies with multi-level exposures can provide valuable insight into the magnitude and direction of study error resulting from losses to follow-up.

Cigarette smoking is a risk factor for Alzheimer's Disease: an analysis controlling for tobacco industry affiliation

To examine the relationship between smoking and Alzheimer's disease (AD) after controlling for study design, quality, secular trend, and tobacco industry affiliation of the authors, electronic databases were searched; 43 individual studies met the inclusion criteria. For evidence of tobacco industry affiliation, http://legacy.library.ucsf.edu was searched. One fourth (11/43) of individual studies had tobacco-affiliated authors. Using random effects meta-analysis, 18 case control studies without tobacco industry affiliation yielded a non-significant pooled odds ratio of 0.91 (95% CI, 0.75-1.10), while 8 case control studies with tobacco industry affiliation yielded a significant pooled odds ratio of 0.86 (95% CI, 0.75-0.98) suggesting that smoking protects against AD. In contrast, 14 cohort studies without tobacco-industry affiliation yielded a significantly increased relative risk of AD of 1.45 (95% CI, 1.16-1.80) associated with smoking and the three cohort studies with tobacco industry affiliation yielded a non-significant pooled relative risk of 0.60 (95% CI 0.27-1.32). A multiple regression analysis showed that case-control studies tended to yield lower average risk estimates than cohort studies (by -0.27 +/- 0.15, P=0.075), lower risk estimates for studies done by authors affiliated with the tobacco industry (by -0.37 +/- 0.13, P=0.008), no effect of the quality of the journal in which the study was published (measured by impact factor, P=0.828), and increasing secular trend in risk estimates (0.031/year +/- 0.013, P=0.02). The average risk of AD for cohort studies without tobacco industry affiliation of average quality published in 2007 was estimated to be 1.72 +/- 0.19 (P< 0.0005). The available data indicate that smoking is a significant risk factor for AD.

Industry-funded research and conflict of interest: an analysis of research sponsored by the tobacco industry through the Center for Indoor Air Research

The Center for Indoor Air Research (CIAR) was created by three United States tobacco companies in 1988. Its stated mission is to fund high-quality, objective research related to indoor air, including studies of environmental tobacco smoke (ETS). Because CIAR is financed by the tobacco industry and funds research related to tobacco, it fosters an inherent conflict of interest. We consider whether this conflict of interest has affected the content, quality, or use of research funded by CIAR. We hypothesize that the tobacco industry might be using CIAR to develop scientific data to support its position that ETS is not harmful to health. CIAR funds two types of projects: "Peer-reviewed" projects are awarded after peer review by a group of scientists, whereas "special-reviewed" projects are awarded directly by tobacco industry executives. CIAR's special-reviewed projects are more likely than its peer-reviewed projects to be related to ETS, to support the tobacco industry position, and to be used by the industry to argue that smoking should not be regulated in public places. Our findings suggest that the tobacco industry is funding special-reviewed projects through CIAR to develop scientific data that it can use in legislative and legal settings. The industry may be financing peer-reviewed projects through CIAR to enhance its credibility, to provide good publicity, and to divert attention from ETS as an indoor air pollutant. CIAR's stated mission of funding high-quality, objective research has been compromised by conflict of interest, and at least some of CIAR's projects are being used to promote the tobacco industry's agenda.