Week 2 Epidemiological Study Designs PDF

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🕶Week 2 : Epidemiological StudyDesignsLearning ObjectivesTo be able to understand the type of questions that might be answered using epidemiological research methods To develop a good understanding of a range of epidemiological study designs, to include Randomised Controlled Trials, Cohort Studies, ...

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Week 2 : Epidemiological Study Designs Learning Objectives To be able to understand the type of questions that might be answered using epidemiological research methods To develop a good understanding of a range of epidemiological study designs, to include Randomised Controlled Trials, Cohort Studies, CaseControl Studies and Cross-Sectional Studies To be able to differentiate between quantitative and qualitative methods and to have an awareness of when they might be used To begin to develop critical appraisal skills and the ability to question sources of evidence and the methods used to obtain them

2.1 Hierarchy of scientific evidence

2.2 Validity What is measurement validity degree to which a measurement measures what it appears to measure What is study validity Degree to which inferences drawn from a study is warranted What is internal validity extent to which a study establishes a trustworthy cause-and-effect relationship between a treatment and an outcome. What is external validity Generalisability, validity of applying the conclusions of a scientific study outside the context of that study. In other words, it is the extent to which the results of a study can be generalized to and across other situations, people, stimuli, and times.

2.3 Observational studies 2.3 A - Descriptive studies No comparison group Bottom of pyramid - very weak evidence e.g. Case report, case series impt in medical sciences - a doctor said that he has observed that he sees a critical SE in babies , he asks other readers if they have noticed the same 2.3 B Analytical studies Cohort studies = Longitudinal Studies = Prospective studies Observational method Population defined as T0 →followed up over period of time (can be years) →exposures and health outcomes of interest is recorded

Prospective : Start at beginning and look forward 5 years later e.g.) Advantage : Large follow up Disadvantage : Lack of control over groups within population - there may be confounding factors

Case-control studies = Retrospective observation studies Start at end point (outcomes) → Look back Record differences in exposure btw 2 or more groups(Cases - with exposure or disease vs Controls - without disease) Advantage : Can study diff exposures that may have led to rare conditions Disadvantage : May be many biases **GOOD FOR rare conditions and historical exposures that are well documented Occupational exposure) or highly memorable (surviving a house fire)

Association between risk factor(exposure) and disease ≠ causal relationship - can have confounding factors

Cross-sectional studies Observational method Represent a 'snapshot' of health picture in population at a given point in time Different samples observed same time Advantage : Useful for estimating prevalence within population

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2.4 Experimental Studies Randomised Controlled Trials Experimental method Participants randomly allocated into 2 or more groups intervention/experimental and control grp Key outcomes f/u throughout study Closely matched in terms of baseline characteristics for good comparisons to be made GOLD STANDARD in hypothesis testing

2.5 Confounding When the effects of 2 associated exposures have not been separated, resulting in interpretation that effect is due to one variable rather than the other the confounder makes the exposure more likely and in some way independently modifies the outcome, making it appear that there is an association between the exposure and the outcome when there is none, or masking a true association Estimated association is not the same as true effect

2.6 Qualitative Data Non numerical information to explore individual or group characteristics w/o using statistical procedures or other quantitative means E.g. Attitudes, Health behaviours, Feedback, Ethics, Values How do you choose an appropriate method? Outcome measures - Validity? Reliability? What are the outcomes of interest? Duration - how long will it take for the outcome to happen / what time period? Controlling variable - can effects of extraneous variables be minimised

2.7 Systematic review and Meta-Analysis Results from multiple studies - precise estimate of tx effect Systematic Review : Quality appraisal, identify an synthesise all published info in a given clinical area Meta Analysis : Pooling results in a statistically valid fashion *but can have bias also Ethics in research Informed consent Confidentiality Respect for human rights Scientific integrity...