Guidelines to Evaluate Human Observational Studies for Quantitative Risk Assessment
Vlaanderen, Jelle, Vermeulen, Roel, Heerderik, Dick, Kromhout, Hans, Environmental Health Perspectives
BACKGROUND: Careful evaluation of the quality of human observational studies (HOS) is required to assess the suitability of HOS for quantitative risk assessment (QRA). In particular, the quality of quantitative exposure assessment is a crucial aspect of HOS to be considered for QRA.
OBJECTIVE: We aimed to develop guidelines for the evaluation of HOS for QRA and to apply these guidelines to case--control and cohort studies on the relation between exposure to benzene and acute myeloid leukemia (AML).
METHODS: We developed a three-tiered framework specific for the evaluation of HOS for QRA and used it to evaluate HOS on the relation between exposure to benzene and AML.
RESULTS: The developed framework consists of 20 evaluation criteria. A specific focus of the frame-work was on the quality of exposure assessment applied in HOS. Seven HOS on the relation of benzene and AML were eligible for evaluation. Of these studies, five were suitable for QRA and were ranked based on the quality of the study design, conduct, and reporting on the study.
CONCLUSION: The developed guidelines facilitate a structured evaluation that is transparent in its application and harmonizes the evaluation of HOS for QRA. With the application of the guidelines, it was possible to identify studies suitable for QRA of benzene and AML and rank these studies based on their quality. Application of the guidelines in QRA will be a valuable addition to the assessment of the weight of evidence of HOS for QRA.
KEYWORDS: benzene, epidemiology, evidence-based medicine, human observational studies, quantitative risk assessment. Environ Health Perspect 116: 1700-1705 (2008). doi: 10.1289/ehp. 11530 available via http://dx/doi.org/[Online 12 August 2008]
Epidemiologic evidence is the most relevant type of evidence for risk assessment, because limited extrapolation is needed to apply study results to a real-life situation. However, because of ethical considerations epidemiologic assessment of risk of potential hazardous exposures is most often limited to observational studies. This deviation from experimental study conditions (e.g., randomized clinical trials) required careful evaluation of the quality of the observational evidence. A major issue in human observational studies (HOS) is the more limited control of circumstances under which studies are performed leading to a potential bias in the estimated association between exposure and health outcome. The quality of the design and conduct of a study affects the potential for bias in the study results and thus the value for risk assessment. In quantitative risk assessment (QRA), exposure--response relations are defined in quantitative terms (i.e., risk per unit of exposure). HOS that conducted quantitative exposure--response analysis (i.e., a quantitative description of the relation between exposure to a hazardous agent and a specific health effect) can contribute directly to QRA. Therefore, the quality of quantitative exposure assessment is crucial to HOS used in QRA. In recent years, several frameworks have been developed to assess the quality of HOS for risk assessment [Goldbohm et al. 2006; Hertz-Picciotto 1995; Money and Margary 2002; Shore et al. 2002; World Health Organization (WHO) Working Group 2000]. These frameworks have provided broad overviews of different aspects that contribute to HOS quality. However, the existing frameworks lack a specific focus on the evaluation of exposure assessment in HOS for QRA. We developed a structured framework with guidelines for the evaluation of HOS in QRA that have a specific focus on the evaluation of the exposure assessment component of HOS. The approach incorporates exclusion of HOS that do not meet the minimal quality required for QRA and ranking based on the quality of the design, conduct, and reporting of the HOS that do meet the minimal quality required fro QRA. Subsequently, to demonstrate its usefulness we applied the framework to all case--control and cohort studies on the relation between exposure to benzene and acute myeloid leukemia (AML). …