Introduction

2017 ◽  
Author(s):  
Mark Elwood
Keyword(s):  
Cohort Studies ◽  
Case Control ◽  
Randomised Trials ◽  
Case Control Studies ◽  
Causal Explanations ◽  
Bradford Hill ◽  
Definition Of ◽  
Meta Analyses ◽  
Observation Bias ◽  
Study Designs

This chapter shows the plan of the book. Later chapters will cover the definition of causation, study designs that can demonstrate causation, how results are presented, the interpretation of studies stressing the non-causal explanations of observation bias, confounding, and chance variation. Then come positive aspects of causation, the Bradford-Hill principles, systematic reviews and meta-analyses, and an overall scheme for assessing studies and diagnosing causation. Further chapters present appraisals of six published studies: randomised trials, cohort studies, and case-control studies. An appendix presents statistical methods with examples.

Study designs which can demonstrate and test causation

2017 ◽  
Author(s):  
Mark Elwood
Keyword(s):  
Cohort Studies ◽  
Case Control ◽  
Control Group ◽  
Case Control Studies ◽  
Retrospective Case ◽  
Community Based ◽  
Cross Sectional ◽  
Healthcare Interventions ◽  
Intervention Trials ◽  
Study Designs

This chapter presents study designs which can test and show causation. Cohort and intervention studies compare people exposed to an agent or intervention with those unexposed or less exposed. Case-control studies compare people affected by a disease or outcome with a control group of unaffected people or representing a total population. Surveys select a sample of people, not chosen by exposure or outcome. Cohort studies may be prospective or retrospective; case-control studies are retrospective; surveys are cross-sectional in time, but retrospective or prospective aspects can be added. In part two, strengths, weaknesses and applications of these designs are shown. Intervention trials, ideally randomised, are the prime method of assessing healthcare interventions; special types include crossover trials and community-based trials. Non-randomised trials are noted. The strengths and weaknesses of cohort studies, case-control studies, and surveys are shown.

Critical Appraisal of Epidemiological Studies and Clinical Trials

2017 ◽  
Author(s):  
Mark Elwood
Keyword(s):  
Cohort Studies ◽  
Statistical Methods ◽  
Critical Appraisal ◽  
Causal Effect ◽  
Internal Validity ◽  
Epidemiological Studies ◽  
Case Control ◽  
Randomised Trials ◽  
Case Control Studies ◽  
Retrospective Cohort Studies

This book presents a system of critical appraisal applicable to clinical, epidemiological and public health studies and to many other fields. It assumes no prior knowledge. The methods are relevant to students, practitioners and policymakers. The book shows how to assess if the results of one study or of many studies show a causal effect. The book discusses study designs: randomised and non-randomised trials, cohort studies, case-control studies, and surveys, showing the presentation of results including person-time and survival analysis, and issues in the selection of subjects. The system shows how to describe a study, how to detect and assess selection biases, observation bias, confounding, and chance variation, and how to assess internal validity and external validity (generalisability). Statistical methods are presented assuming no previous knowledge, and showing applications to each study design. Positive features of causation including strength, dose-response, and consistency are discussed. The book shows how to do systematic reviews and meta-analyses, and discusses publication bias. Systems of assessing all evidence are shown, leading to a general method of critical appraisal based on 20 key questions in five groups, which can be applied to any type of study or any topic. Six chapters show the application of this method to randomised trials, prospective and retrospective cohort studies, and case-control studies. An appendix summarises key statistical methods, each with a worked example. Each main chapter has self-test questions, with answers provided.

Consumption of Artificially-sweetened Soft Drinks and Risk of Gastrointestinal Cancer: A Meta-analysis of Observational Studies

2021 ◽  
pp. 1-50
Author(s):  
Alfred Jatho ◽  
Jansen Marcos Cambia ◽  
Seung-Kwon Myung ◽  
Keyword(s):  
Cohort Studies ◽  
Observational Studies ◽  
Meta Analysis ◽  
Epidemiological Studies ◽  
Case Control ◽  
Soft Drinks ◽  
Case Control Studies ◽  
Gi Cancer ◽  
Increased Risk ◽  
Meta Analyses

Abstract Objective: There remain inconclusive findings from previous observational epidemiological studies on whether consumption of artificially-sweetened soft drinks (ASSDs) increases the risk of gastrointestinal (GI) cancer. We investigated the associations between the consumption of ASSDs and the risk of GI cancer using a meta-analysis. Design: Systematic review and meta-analysis. Setting: PubMed and EMBASE were searched using keywords until May 2020 to identify observational epidemiological studies on the association between the consumption of ASSDs and the risk of GI cancer. Subjects: Twenty-one case-control studies and 17 cohort studies with 12,397 cancer cases and 2,474,452 controls. Results: In the random-effects meta-analysis of all the studies, consumption of ASSDs was not significantly associated with the risk of overall GI cancer (odds ratio (OR)/relative risk (RR), 1.02; 95% CI, 0.92-1.14). There was no significant association between the consumption of ASSDs and the risk of overall GI cancer in the subgroup meta-analyses by study design (case-control studies: OR, 0.95; 95% CI, 0.82-1.11; cohort studies: RR, 1.14; 95% CI, 0.97-1.33). In the subgroup meta-analysis by type of cancer, consumption of ASSDs was significantly associated with the increased risk of liver cancer (OR/RR, 1.28; 95% CI,1.03-1.58). Conclusions: The current meta-analysis of observational epidemiological studies suggests that overall, there is no significant association between the consumption of ASSDs and the risk of GI cancer.

scholarly journals Research made Easy: Answering Important Questions with Valid Designs

2012 ◽  
Vol 46 (1) ◽  
pp. 8-11
Author(s):  
Harman Chaudhry ◽  
Mohit Bhandari
Keyword(s):  
Clinical Study ◽  
Cohort Studies ◽  
Case Reports ◽  
Research Question ◽  
Case Control ◽  
Controlled Trials ◽  
Case Control Studies ◽  
Randomized Controlled ◽  
Observational Cohort ◽  
Study Designs

ABSTRACT Clinical research fundamentally involves finding answers to questions. Next to asking important questions, determining what type of study design to use is arguably the most pivotal step for a researcher. In this article, we provide an overview of various clinical study designs, including case reports and series, case-control studies, observational cohort studies, randomized controlled trials and systematic reviews. We aim to elucidate the utility, advantages and drawbacks of these study designs in order to assist researchers in selecting the most valid design for their research question. How to cite this article Chaudhry H, Bhandari M. Research made Easy: Answering Important Questions with Valid Designs. J Postgrad Med Edu Res 2012;46(1):8-11

Introduction to epidemiological study designs

2020 ◽  
pp. 83-98
Author(s):  
Tamsin Ford ◽  
Jayati Das-Munshi ◽  
Martin Prince
Keyword(s):  
Mixed Methods ◽  
Data Collection ◽  
Cohort Studies ◽  
Epidemiological Study ◽  
Study Design ◽  
Case Control ◽  
Psychiatric Epidemiology ◽  
Case Control Studies ◽  
Cross Sectional ◽  
Study Designs

This chapter provides a brief overview for each of the main types of study design commonly used in psychiatric epidemiology. The chapter begins with a discussion of the importance of study design. This is followed by a section on classifying study design, including descriptive studies, ecological studies, cross-sectional surveys, cohort studies, case–control studies, intervention studies, and qualitative and mixed methods studies. The chapter concludes with a description of the basic steps which should be observed in the conduct of studies employing quantitative methodologies (including cross-sectional, cohort, and case–control studies), as well as discussing interviews/assessments, and data collection and processing.

Nonsteroidal anti-inflammatory drugs and incidence of atrial fibrillation: a meta-analysis

QJM ◽  
2020 ◽  
Vol 113 (2) ◽  
pp. 79-85 ◽  
Author(s):  
R Chokesuwattanaskul ◽  
K Chiengthong ◽  
C Thongprayoon ◽  
P Lertjitbanjong ◽  
T Bathini ◽  
...  
Keyword(s):  
Atrial Fibrillation ◽  
Systematic Review ◽  
Cohort Studies ◽  
Meta Analysis ◽  
Random Effect ◽  
Case Control ◽  
Case Control Studies ◽  
Inflammatory Drugs ◽  
Anti Inflammatory ◽  
Meta Analyses

Abstract Background Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used for many inflammatory disorders and pain-related illnesses. Despite their widespread use, the association between NSAIDs and the incidence of atrial fibrillation (AF) remains unclear. The aim of this systematic review and meta-analysis is to investigate this association. Methods A systematic review was conducted in MEDLINE, EMBASE and Cochrane databases from inception through August 2019 to identify studies that evaluated the risk of AF among patients using NSAIDs. Pooled risk ratios (RRs) and 95% CI were calculated using a random-effect, generic inverse variance method. The protocol for this meta-analysis is registered with PROSPERO (International Prospective Register of Systematic Reviews; no. CRD42019141609). Results Eight observational studies (four case–control studies and four cohort studies) with a total of 14 806 420 patients were enrolled. When compared with nonNSAIDs users, the pooled RR of AF in patients with NSAIDs use was 1.29 (95% CI 1.19–1.39). Meta-analyses based on the type of study were additionally performed. Subgroup analysis by study design revealed a significant association between the use of NSAIDs and AF for both case–control studies (pooled RR 1.37; 95% CI, 1.15–1.63) and cohort studies (pooled RR 1.22; 95% CI, 1.14–1.31). Sub-analyses based on specific NSAIDs showed pooled RRs of AF in patients using ibuprofen of 1.30 (95% CI 1.22–1.39), naproxen of 1.44 (95% CI 1.18–1.76) and diclofenac of 1.37 (95% CI 1.10–1.71), respectively. Funnel plot and Egger’s regression asymmetry tests were performed and showed no publication bias. Conclusion NSAID use is associated with incident AF. Our study also demonstrated a consistent result among different NSAIDs.

Ethnic differences in risk factors for subarachnoid hemorrhage

2007 ◽  
Vol 107 (3) ◽  
pp. 522-529 ◽  
Author(s):  
Vibhor Krishna ◽  
Dong H. Kim
Keyword(s):  
Risk Factors ◽  
Subarachnoid Hemorrhage ◽  
Alcohol Consumption ◽  
Cohort Studies ◽  
Odds Ratio ◽  
Case Control ◽  
Ethnic Composition ◽  
Effect Estimate ◽  
Case Control Studies ◽  
Current Smoking

Object Studies on risk factors for subarachnoid hemorrhage (SAH) show heterogeneity. For example, hypertension has been found to be a significant risk factor in some studies but not in others. The authors hypothesized that differences in the ethnicity of the populations studied could account for these findings. Methods A metaanalysis was performed using 17 case-control and 10 cohort studies that met specified inclusion criteria. The authors used a random-effect model to calculate the pooled effect estimates for current smoking, hypertension, and alcohol consumption. A meta–regression analysis was performed using the ethnic composition of the study populations as a covariate. Studies were classified as multiethnic or monoethnic, and the pooled effect estimates were compared. Results Analysis of the cohort studies yielded a pooled effect estimate or risk ratio of 3.18 (95% confidence interval [CI] 2.37–4.26) for current smoking, 3.05 (95% CI 2.09–4.44) for hypertension, and 2.46 (95% CI 1.42–4.24) for alcohol consumption at a rate of 150 g/week or more. The results were similar for the case-control studies. For current smoking, the ethnic composition of the study population was a statistically significant predictor of heterogeneity among case-control studies (p < 0.001, even after application of the Bonferroni correction). The risk for SAH among current smokers was higher in multiethnic populations (odds ratio 3.832) than in monoethnic populations (odds ratio 2.487). Conclusions The results of this metaanalysis suggest that differences in susceptibility to the harmful health effects of smoking may be one cause of the observed differences in SAH incidence for different ethnic groups. The role of ethnicity in risk factors for SAH should be considered in future studies.

Soy Consumption with Risk of Coronary Heart Disease and Stroke: A Meta-Analysis of Observational Studies

2016 ◽  
Vol 46 (4) ◽  
pp. 242-252 ◽  
Author(s):  
Danfei Lou ◽  
Yuehua Li ◽  
Guoliang Yan ◽  
Jianhong Bu ◽  
Haihui Wang
Keyword(s):  
Coronary Heart Disease ◽  
Heart Disease ◽  
Cohort Studies ◽  
Observational Studies ◽  
Meta Analysis ◽  
Case Control ◽  
Inverse Association ◽  
Case Control Studies ◽  
Relative Risks ◽  
Product Consumption

Background: The association of soy product consumption with the relative risk of cardiovascular disease remains controversial. This meta-analysis aimed at investigating whether an association exists between soy consumption and the risk of stroke and coronary heart disease (CHD) in observational studies. Methods: A systematic search of the PubMed and EMBASE databases was performed for case-control and cohort studies that assessed soy consumption and the risk of stroke and CHD. Summary relative risks (SRRs) and 95% CIs were combined by using a random-effects model. Results: Of a total of 1,266 abstracts, 5 prospective cohort and 6 case-control studies met our inclusion criteria, and comprised 4,954 stroke and 7,616 CHD events. Based on the high vs. low analyses, combining cohort studies showed no association between soy intake and risk of stroke (SRR 0.92; 95% CI 0.70-1.10; Pheterogeneity = 0.236; I2 = 29.4%) or CHD (SRR 0.97; 95% CI 0.74-1.27; Pheterogeneity = 0.020; I2 = 62.7%), although a significantly inverse association between soy intake and the risk of stroke (SRR 0.54; 95% CI 0.34-0.87; Pheterogeneity = 0.001; I2 = 79.3%) and CHD (SRR 0.66; 95% CI 0.56-0.77; Pheterogeneity = 0.421; I2 = 0) was observed in case-control studies. No association between soy isoflavone intake and the risk of stroke and CHD was identified. Conclusion: There was limited evidence to indicate that soy consumption was inversely associated with the risk of stroke and CHD, although further studies, with prospective designs that use validated questionnaires and control for important confounders, are warranted.

scholarly journals A probability model for evaluating the bias and precision of influenza vaccine effectiveness estimates from case-control studies

2014 ◽  
Vol 143 (7) ◽  
pp. 1417-1426 ◽  
Author(s):  
M. HABER ◽  
Q. AN ◽  
I. M. FOPPA ◽  
D. K. SHAY ◽  
J. M. FERDINANDS ◽  
...  
Keyword(s):  
Influenza Vaccine ◽  
Medical Care ◽  
Randomized Clinical Trials ◽  
Probability Model ◽  
Control Design ◽  
Case Control ◽  
Vaccine Effectiveness ◽  
Case Control Studies ◽  
Respiratory Illnesses ◽  
Study Designs

SUMMARYAs influenza vaccination is now widely recommended, randomized clinical trials are no longer ethical in many populations. Therefore, observational studies on patients seeking medical care for acute respiratory illnesses (ARIs) are a popular option for estimating influenza vaccine effectiveness (VE). We developed a probability model for evaluating and comparing bias and precision of estimates of VE against symptomatic influenza from two commonly used case-control study designs: the test-negative design and the traditional case-control design. We show that when vaccination does not affect the probability of developing non-influenza ARI then VE estimates from test-negative design studies are unbiased even if vaccinees and non-vaccinees have different probabilities of seeking medical care against ARI, as long as the ratio of these probabilities is the same for illnesses resulting from influenza and non-influenza infections. Our numerical results suggest that in general, estimates from the test-negative design have smaller bias compared to estimates from the traditional case-control design as long as the probability of non-influenza ARI is similar among vaccinated and unvaccinated individuals. We did not find consistent differences between the standard errors of the estimates from the two study designs.

scholarly journals Relevance of hMLH1 -93G>A, 655A>G and 1151T>A polymorphisms with colorectal cancer susceptibility: a meta-analysis based on 38 case-control studies

2018 ◽  
Vol 64 (10) ◽  
pp. 942-951 ◽  
Author(s):  
Mohammad Zare ◽  
Jamal Jafari-Nedooshan ◽  
Mohammadali Jafari ◽  
Hossein Neamatzadeh ◽  
Seyed Mojtaba Abolbaghaei ◽  
...  
Keyword(s):  
Colorectal Cancer ◽  
Cancer Susceptibility ◽  
Meta Analysis ◽  
Asian Population ◽  
Case Control ◽  
Biomedical Literature ◽  
Case Control Studies ◽  
Increased Risk ◽  
Comprehensive Search ◽  
Meta Analyses

SUMMARY OBJECTIVE: There has been increasing interest in the study of the association between human mutL homolog 1 (hMLH1) gene polymorphisms and risk of colorectal cancer (CRC). However, results from previous studies are inconclusive. Thus, a meta-analysis was conducted to derive a more precise estimation of the effects of this gene. METHODS: A comprehensive search was conducted in the PubMed, EMBASE, Chinese Biomedical Literature databases until January 1, 2018. Odds ratio (OR) with 95% confidence interval (CI) was used to assess the strength of the association. RESULTS: Finally, 38 case-control studies in 32 publications were identified met our inclusion criteria. There were 14 studies with 20668 cases and 19533 controls on hMLH1 −93G>A, 11 studies with 5,786 cases and 8,867 controls on 655A>G and 5 studies with 1409 cases and 1637 controls on 1151T>A polymorphism. The combined results showed that 655A>G and 1151T>A polymorphisms were significantly associated with CRC risk, whereas −93G>A polymorphism was not significantly associated with CRC risk. As for ethnicity, −93G>A and 655A>G polymorphisms were associated with increased risk of CRC among Asians, but not among Caucasians. More interestingly, subgroup analysis indicated that 655A>G might raise CRC risk in PCR-RFLP and HB subgroups. CONCLUSION: Inconsistent with previous meta-analyses, this meta-analysis shows that the hMLH1 655A>G and 1151T>A polymorphisms might be risk factors for CRC. Moreover, the −93G>A polymorphism is associated with the susceptibility of CRC in Asian population.

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