Observational studiesPub Date : 2026-08-27eCollection Date: 2026-01-01DOI: 10.1353/obs.00011
Gary C N Hettinger, Audrey Renson, Herbert P Susmann, Iván Díaz
{"title":"Beyond \"No Unmeasured Confounding\": Challenges and Opportunities for Cornfield-Style Reasoning in Modern Causal Inference.","authors":"Gary C N Hettinger, Audrey Renson, Herbert P Susmann, Iván Díaz","doi":"10.1353/obs.00011","DOIUrl":"10.1353/obs.00011","url":null,"abstract":"<p><p>Jerome Cornfield's (1959) analysis of smoking and lung cancer introduced a foundational principle for causal inference from observational data: causal conclusions should be evaluated not by the absence of assumption violations, but by the implausibility of the violations required to overturn them. In the decades since, causal inference research has made substantial progress in explicitly defining identification assumptions and improving estimation under those assumptions. As estimation theory has advanced, concerns about model misspecification have receded, and flexible semi-parametric methods now exist for increasingly complex causal questions. Despite this progress, there has been comparatively little success in extending Cornfield-style sensitivity analysis to these modern settings, limiting both the interpretability and practical adoption of contemporary causal methods. In this commentary, we revisit Cornfield's original framework and consider its amenability for four identification assumptions that have received growing attention beyond standard unmeasured confounding: positivity, interference, parallel trends, and sequential exchangeability. For each, we evaluate its accessibility to Cornfield-style reasoning, discussing challenges and opportunities for developing interpretable, calibrated sensitivity analyses. We argue that Cornfield-style reasoning is more naturally applicable to some assumptions than others, clarifying where such approaches are promising and where fundamental obstacles remain.</p>","PeriodicalId":74335,"journal":{"name":"Observational studies","volume":"12 2","pages":"261-278"},"PeriodicalIF":0.0,"publicationDate":"2026-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13600448/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149042544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Observational studiesPub Date : 2026-08-27eCollection Date: 2026-01-01DOI: 10.1353/obs.00009
Melody Huang, Samuel D Pimentel
{"title":"Getting to Know Worst-Case Confounders.","authors":"Melody Huang, Samuel D Pimentel","doi":"10.1353/obs.00009","DOIUrl":"10.1353/obs.00009","url":null,"abstract":"<p><p>Since Cornfield, Haenszel, Hammond, Lilienfeld, Shimkin, and Wynder (1959)'s seminal contribution, many sensitivity analyses have been introduced. Modern-day approaches to sensitivity analysis aim to impose relatively little structure on the unobserved confounder. However, while a sensitivity analysis may not rely on many assumptions on the unobserved confounder, the worst-case bounds that are solved for within a sensitivity analysis are often only realized when a hypothetical confounder takes on a specific form, which is not always made explicit. In the following commentary, we consider several leading sensitivity analysis approaches and review what is known about the structure of the confounder at which the worst-case bounds are realized. We show that the type of sensitivity model used can induce different data generating processes for the worst-case confounders. We argue that understanding the structure of the omitted confounder implied by the worst-case bounds is crucial for more transparent sensitivity analysis, and we suggest directions for future work.</p>","PeriodicalId":74335,"journal":{"name":"Observational studies","volume":"12 2","pages":"233-246"},"PeriodicalIF":0.0,"publicationDate":"2026-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13600455/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149042580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Observational studiesPub Date : 2026-08-27eCollection Date: 2026-01-01DOI: 10.1353/obs.00002
Joel B Greenhouse, Christopher J Phillips
{"title":"Commentary: Smoking and Lung Cancer: A Historical Perspective.","authors":"Joel B Greenhouse, Christopher J Phillips","doi":"10.1353/obs.00002","DOIUrl":"10.1353/obs.00002","url":null,"abstract":"<p><p><i>Smoking and Lung Cancer</i> (1959) is a compelling case study of the nature of proof and causation in medicine. It should be understood as the culmination of years of work to find rigorous methods for making statistically and rhetorically convincing accounts of how associations might be deemed to be causal. In this comment, we highlight several papers written during the 1950s by Jerome Cornfield that illustrate the role he played in laying the groundwork for this important and influential work.</p>","PeriodicalId":74335,"journal":{"name":"Observational studies","volume":"12 2","pages":"145-154"},"PeriodicalIF":0.0,"publicationDate":"2026-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13600452/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149042565","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Observational studiesPub Date : 2026-08-27eCollection Date: 2026-01-01DOI: 10.1353/obs.00013
Qingyan Xiang, Jiahao Zhang, Bojian Feng
{"title":"Using Large Language Models for Sensitivity Analysis in Causal Inference: Case Studies on Cornfield's Inequality and the E-Value.","authors":"Qingyan Xiang, Jiahao Zhang, Bojian Feng","doi":"10.1353/obs.00013","DOIUrl":"https://doi.org/10.1353/obs.00013","url":null,"abstract":"<p><p>Sensitivity analysis methods such as the Cornfield's inequality and the E-value were developed to assess the robustness of observed associations against unmeasured confounding - a major challenge in observational studies. However, the calculation and interpretation of these methods can be difficult for clinicians and interdisciplinary researchers. Recent advances in large language models (LLMs) offer accessible tools that could assist sensitivity analyses, but their reliability in this context has not been studied. We assess four widely used LLMs, ChatGPT, Claude, DeepSeek, and Gemini, on their ability to conduct sensitivity analyses using the Cornfield's inequality and the E-value. We first extract study-specific information (exposures, outcomes, measured confounders, and effect estimates) from four published observational studies in different fields. Using such information, we develop structured prompts to assess the performance of the LLMs in three aspects: (1) accuracy of E-value calculation, (2) qualitative interpretation of robustness to unmeasured confounding, and (3) suggestion of possible unmeasured confounders. To our knowledge, there has been little prior work on using LLMs for sensitivity analysis, and this study is an early investigation in this area. The results show that ChatGPT, Claude, and Gemini accurately reproduce the E-values, whereas DeepSeek shows small biases. Qualitative conclusions from all the LLMs align with the magnitude of the E-values and the reported effect sizes, and all models identify biologically and epidemiologically plausible unmeasured confounders. These findings suggest that, when guided by structured prompts, LLMs can effectively assist in evaluating unmeasured confounding, and thereby can support study design and decision-making in observational studies.</p>","PeriodicalId":74335,"journal":{"name":"Observational studies","volume":"12 2","pages":"297-310"},"PeriodicalIF":0.0,"publicationDate":"2026-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13600449/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149042709","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Observational studiesPub Date : 2026-08-27eCollection Date: 2026-01-01DOI: 10.1353/obs.00004
Kenneth A Frank, Qinyun Lin, Spiro J Maroulis
{"title":"Cornfield's Pragmatic Contribution to Policy Discourse: Continued.","authors":"Kenneth A Frank, Qinyun Lin, Spiro J Maroulis","doi":"10.1353/obs.00004","DOIUrl":"10.1353/obs.00004","url":null,"abstract":"<p><p>Cornfield et al.'s contributions included documenting epidemiological and policy debates regarding the effects of smoking on lung cancer. It was in the context of those debates that Cornfield et al. expressed sensitivity of the estimated effect of smoking to the dual components of confounding-relationship of a potential confounder (e.g., genes) to smoking (the focal predictor) and to lung cancer (the outcome). Current advancements have used various graphical and tabular representations to similarly express sensitivity to the dual components of confounding. As a representative of these advancements, we present Frank's Impact Threshold for a Confounding (ITCV), which resolves the dual components of confounding into a single term based on the product of the confounder's correlations with the focal predictor and with the outcome. We calculate the ITCV for an inference of an effect of kindergarten retention on achievement and provide benchmarks based on observed covariates to interpret the ITCV. Ultimately, any sensitivity analysis should only be applied after one has estimated the best possible model. The value of the sensitivity analysis is then to inform policy-oriented discourse among as wide a range of stakeholders as possible.</p>","PeriodicalId":74335,"journal":{"name":"Observational studies","volume":"12 2","pages":"163-178"},"PeriodicalIF":0.0,"publicationDate":"2026-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13600451/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149042582","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Observational studiesPub Date : 2026-08-27eCollection Date: 2026-01-01DOI: 10.1353/obs.00006
Richard J Cook, Laura S Bumbulis, Sung Duk Kim, Paul S Albert
{"title":"Modeling the Effects of Smoking on Lung Cancer.","authors":"Richard J Cook, Laura S Bumbulis, Sung Duk Kim, Paul S Albert","doi":"10.1353/obs.00006","DOIUrl":"10.1353/obs.00006","url":null,"abstract":"<p><p>Modeling the effect of smoking on the risk of lung cancer in cohort studies requires specification of time-dependent exposure variables and appropriate handling of confounding. This can be challenging as data on both exposure and confounders are typically incompletely observed. We discuss population exposure and disease processes and review modeling challenges when exposures are dynamic and challenging to summarize. Biases arising from failure to address time-dependent confounding are highlighted, with particular reference to a paradox related to the effect of quitting on risk of lung cancer. We stress the utility of comprehensive joint models.</p>","PeriodicalId":74335,"journal":{"name":"Observational studies","volume":"12 2","pages":"193-210"},"PeriodicalIF":0.0,"publicationDate":"2026-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13600457/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149042547","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Observational studiesPub Date : 2026-08-27eCollection Date: 2026-01-01DOI: 10.1353/obs.00012
Brian Knaeble, Qinyun Lin, Erich Kummerfeld, Kenneth A Frank
{"title":"Sensitivity Analysis of the Consistency Assumption.","authors":"Brian Knaeble, Qinyun Lin, Erich Kummerfeld, Kenneth A Frank","doi":"10.1353/obs.00012","DOIUrl":"10.1353/obs.00012","url":null,"abstract":"<p><p>Sensitivity analysis informs causal inference by assessing the sensitivity of conclusions to departures from assumptions. The consistency assumption states that there are no hidden versions of treatment and that the outcome arising naturally equals the outcome arising from intervention. When reasoning about the possibility of consistency violations, it can be helpful to distinguish between covariates and versions of treatment. In the context of surgery, for example, genomic variables are covariates and the skill of a particular surgeon is a version of treatment. There may be hidden versions of treatment, and this paper addresses that concern with a new kind of sensitivity analysis. Whereas many methods for sensitivity analysis are focused on confounding by unmeasured covariates, the methodology in this paper is focused on confounding by hidden versions of treatment. In this paper, new mathematical notation is introduced to support the novel method, and example applications are described.</p>","PeriodicalId":74335,"journal":{"name":"Observational studies","volume":"12 2","pages":"279-296"},"PeriodicalIF":0.0,"publicationDate":"2026-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13600454/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149042619","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Observational studiesPub Date : 2026-08-27eCollection Date: 2026-01-01DOI: 10.1353/obs.00010
Elena Stanghellini, Sara Geneletti
{"title":"Sensitivity Analysis on the Odds Ratio Scale: Extending Cornfield's Conditions.","authors":"Elena Stanghellini, Sara Geneletti","doi":"10.1353/obs.00010","DOIUrl":"10.1353/obs.00010","url":null,"abstract":"<p><p>Two procedures are proposed to assess sensitivity to a binary unobserved confounder for a binary outcome when the causal effect is expressed as a (log) odds ratio, as commonly arises in standard logistic modelling, particularly in case-control studies. The methods are based on graphical tools that visualize the extent to which an unobserved confounder could attenuate, nullify, or even reverse the estimated causal effect. The second procedure relies on a single sensitivity parameter, yielding a naturally bounded assessment that can be translated into an objective measure. Connections with Cornfield's conditions on relative risks are presented, thereby enlarging the circumstances where the proposed procedures can be applied and establishing a link that allows extensions to polytomous confounders.</p>","PeriodicalId":74335,"journal":{"name":"Observational studies","volume":"12 2","pages":"247-260"},"PeriodicalIF":0.0,"publicationDate":"2026-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13600446/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149042632","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Observational studiesPub Date : 2026-08-27eCollection Date: 2026-01-01DOI: 10.1353/obs.00014
Elizabeth Willow Eisenhauer, Daifeng Han, Brad Edwards, J Michael Brick
{"title":"Toward a Total Causal Error Framework: Extending Cornfield's Insights Across Causal Identification, Representation, and Measurement.","authors":"Elizabeth Willow Eisenhauer, Daifeng Han, Brad Edwards, J Michael Brick","doi":"10.1353/obs.00014","DOIUrl":"10.1353/obs.00014","url":null,"abstract":"<p><p>Cornfield et al.'s (1959) analysis of smoking and lung cancer showed how explicit assumptions about unobserved confounding and selection mechanisms shape the boundary between statistical association and causal conclusions. Today, causal inference spans diverse fields including economics, statistics, psychology, epidemiology, and evaluation, with distinct traditions and tools. Without a shared framework, it can be difficult to accumulate evidence across studies or to diagnose why results differ when similar questions are studied independently, particularly when differences arise from upstream design and data-generation choices rather than analytic methods alone. While tools for causal identification such as Directed Acyclic Graphs (DAGs) have become widely used across disciplines, they do not naturally foreground threats arising from representation and measurement errors. In contrast, the Total Survey Error (TSE) framework enumerates representation and measurement errors across the survey life cycle and is routinely used to evaluate tradeoffs in survey design and data collection. We propose a Total Causal Error (TCE) framework that integrates causal inference with the TSE perspective to organize risks to causal conclusions along parallel paths of causal identification, representation, and measurement, across the stages of the theoretical estimand, empirical estimand, data collection, data processing, and estimation and interpretation. We propose a version of this framework, provide explicit definitions for its components, illustrate a small number of use cases, and invite further development and coordination across fields.</p>","PeriodicalId":74335,"journal":{"name":"Observational studies","volume":"12 2","pages":"311-322"},"PeriodicalIF":0.0,"publicationDate":"2026-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13600453/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149042603","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}