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Nutr08009 l3
- 1. EPIDEMIOLOGY AND CONTROVERSIES IN NUTRITION: ASSESSING EVIDENCE LECTURER: ROSEMARY STAMM CURRENT ISSUESIN FOODAND NUTRITION
- 2. RCT SystematicReviews Meta-analyses Cohort studies Case-control studies Cross-sectional studies Animal studies and expert opinion Qualityofevidence }Observational studies
- 3. Animal studies and expert opinion Considered the lowest level of evidence Animal studies provide mechanistic data but may not apply to humans Expert opinion can be biased unless based on higher levels of evidence, i.e. systematic reviews or meta-analyses
- 4. Observational studies Studies where a population sample or groups are observed, but there is no intervention Includes cross-sectional, case-control, and cohort studies Subject to confounding However, may be the most appropriate study design for many studies involving diet and nutrition Important for study design to address confounders Selection of representative population samples Statistical adjustment for confounders
- 5. Confounding When the dependent variable (diet or nutrient) is associated with another confounding variable than can affect the outcome variable (e.g. cardiovascular disease risk, cancer risk etc.) Smoking Alcohol Socioeconomic status BMI Age Sex
- 6. Cross-sectional studies Data is collected from a sample of a population group at a single point in time Small cross-sectional studies determining associations Can be used to determine prevalence in populations Includes data collected from national surveys NANS - National Adult Nutrition Survey, Ireland 2008-10 NDNS - National Diet and Nutrition Survey, UK rolling survey NHANES - National Health and Nutrition Examination Survey, US rolling survey
- 8. Case-control studies Typically reserved for studies involving diseases or outcomes that are very rare Control participants are selected from the general population and matched to cases through age, sex, and other potentially confounding variables Retrospective analysis of exposure variable Odds ratio is calculated to determine disease risk Odds ratio is an estimate of relative risk when the total population is unknown
- 9. Cohort studies Exposure Disease/Outcome No Disease/Outcome Disease/Outcome No Disease/Outcome No exposure
- 10. Cohort studies Prospective - take a group and define the exposure then monitor the disease/outcome over time Prospective cohort studies may last decades Retrospective - take a group and define by disease/outcome and retrospectively assess the exposure (i.e. look back in time) Retrospective cohort studies are subject to poor recall and recall bias Confounding variables require adjustment in statistical analysis
- 11. Cohort studies EPIC The European Prospective Investigation into Cancer and Nutrition (EPIC) is a prospective cohort with more than 521 000 study participants enrolled from 23 centres in 10 western European countries. Nurses' Health Study Starting with the original Nurses’ Health Study in 1976, the studies are now in their third generation with Nurses’ Health Study 3 (which is still enrolling male and female nurses) and count more than 275,000 participants.
- 12. Randomised-controlled trials (RCT) Considered the gold-standard research study design Chances of bias are reduced because any confounding variables should be randomly distributed in both the treatment and placebo groups Many nutritional studies cannot be answered by RCT design studies What are some reasons that nutritional studies cannot be conducted using RCT designs?
- 13. Meta-analyses Statistical analysis of data from multiple studies Help to identify heterogeneity in results (i.e. when conflicting results are reported by different studies) Increase sample size and therefore statistical power to detect associations Give more precise estimates of an effect
- 14. Meta- analyses
- 15. Systematicreviews Review of scientific literature that is carried out in a specific and methodical way Narrow research question Search strategy is defined, systematic, and often performed in duplicate Methods and specific outcomes are defined Involves some form of quality assessment of studies or sensitivity analysis of exclusion of potentially biased reports Results presented categorically by study type/characteristics Conclusion is evidence-based
- 17. Systematicreviews Researchers conducting systematic reviews use explicit, systematic methods that are selected with a view aimed at minimizing bias, to produce more reliable findings to inform decision-making. Cochrane Reviews are updated to reflect the findings of new evidence when it becomes available https://www.cochranelibrary.com/
- 18. Reporting guidelines for studies www.equator-network.org STROBE-nut PRISMACONSORTSTROBE A collection of reporting guidelines for studies of different designs Aim to improve the reliability and value of published health research literature Promoting transparent and accurate reporting and wider use of robust reporting guidelines
- 19. Reporting guidelines for studies STROBE-nut PRISMA CONSORT STROBE Strengthening The Reporting of OBservational Studies in Epidemiology – nutritional epidemiology CONsolidated Standards Of Reporting Trials Preferred Reporting Items for Systematic Reviews and Meta-Analyses
- 20. Assessing the quality of studies Is the study sample representative of the population of interest? What are the eligibility criteria? What is the sample size? Is the calculation of sample size explained in the methods? What measures have been taken to address potential sources of bias? In the methods? In the discussion? Is bias addressed in the methods for dietary assessment? Is heterogeneity addressed?
- 21. Canyouthinkofimportantconfoundingvariablesthathaven'tbeenaddressed? Does the information within the introduction and discussion reflect the scientific literature? Are the exposure and outcome variables well defined? What are the sources of funding? Is information included on non-respondents and dropouts from the study? Assessing the quality of studies