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- 1. STUDY DESIGNS Ephron Ephraim Yerembede, B.MLS, M.Sc. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 1
- 2. • Describe the differences between observational and experimental study designs • List and describe the different sub-types of study designs with strengths and weaknesses of each type of study design • Identify ideal study designs for particular situations • List and explain the Bradford Hill Criteria for causality Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 2 Learning Objectives
- 3. • A road map or blueprint and strategy of investigation so conceived to find answers to research questions or problems as objectively, validly, accurately, and economically as possible • Study designs direct how the investigation/research is conducted Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 3 Definition
- 4. • Research questions • Research goals • Research philosophy and paradigms • Ontology – what is reality? • Epistemology – How can I know reality? • Methodology – how do you go about finding out? • Methods – what techniques do you use to find out? • Researcher skills • Time and funds Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 4 Factors to consider
- 5. Classification of Study Designs Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Study Design Observational Descriptive Case report/Case series Cross-sectional Surveys Analytical Case control Cohort Experimental RCCT RCFT Ecological 5
- 6. • Observational: Investigator does not assign exposure; they merely observe phenomena in their natural settings • Descriptive • Analytical • Experimental: This involves manipulation of the exposure and randomization of study subjects to two or more groups, usually treatment and control • The main aim of various study designs: - Descriptive studies: to generate/formulate hypothesis. - Analytical studies: to test hypothesis. - Experimental studies: to prove hypothesis. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 6 Principle
- 7. Observational Study Investigator is passive; has no control over exposure • Descriptive: used to describe the occurrence of disease or health outcomes in a specific population or study group; basically, 3 questions are asked when, where, and who i.e., time, place, and person distribution. - Case reports/case series - Cross-sectional - Ecological • Analytical: describe the association between exposure and outcome - Case-control - Cohort Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 7
- 8. • Describe in-depth the presenataion of a single case • Generally, report a new or unique finding, e.g., - previously undescribed disease - unexpected new therapeutic effect - adverse events (drug reaction) Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 8 Case Reports
- 9. • Furnishes information about exposures, outcomes, and other variables of interest among multiple similar cases • Experience of a group of patients with a similar diagnosis • Cases may be identified from a single or multiple sources • Generally, report on new/unique condition • May be the only realistic design for bizarre disorders/diseases Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 9 Case Series
- 10. Advantages • Good for hypothesis generation • Provides information for very rare diseases with few established risk factors • Characterizes averages for disorders Disadvantages • Cannot study cause-and-effect relationships • Cannot assess disease frequency Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 10
- 11. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Case Report Case Series One case of unusual findings Multiple cases of unusual findings 11
- 12. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 • An observational study and the investigator has no control over the exposure of interest (e.g., diet). • It includes identifying a defined population at a particular point in time, measuring a range of variables on an individual basis, and at the same time measuring the outcome of interest. • A design that looks at exposure and disease status at a single point in time (a cross-section of the population) “A Snapshot” 12 Cross-sectional Study
- 13. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Cross-sectional Design (comparative) time Study only exists at this point in time Study population No Disease Disease factor present factor absent factor present factor absent 13
- 14. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Uses • Measures disease burden and exposure to risk factors • Compare the prevalence of disease in populations • Understand the distribution of a health problem by time, place, person - Plan healthcare delivery services • Generate hypothesis • Examine evolving trends - before/after survey - iterative cross-sectional survey 14 Cross-sectional Study
- 15. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Advantages • Relatively quick and easier to perform • Less expensive Disadvantages • It measures prevalence only • It can not measure incidence • Prevalent cases are survivors • The temporal relationship may be difficult to establish • Cannot specify disease etiology 15 Cross-sectional Study
- 16. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 • Conducted when individual-level data would be difficult or impossible to collect - e.g., effect of air pollution - Legislation • Useful for: - Correlating population disease rates with factors of interest, such as healthcare use - Demonstrating changes in mortality over time (time series) - Comparing the prevalence of a disease between different regions at a single point in time (geographical studies) • The unit of analysis is the population 16 Ecological study
- 17. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 • Case-control studies are relatively simple and cheap • They include cases (people with disease of interest) and a suitable control group (people without that disease or outcome variable). • The occurrence of the possible exposure is compared between cases and controls. • Case-control studies are also called retrospective studies since the investigator is looking backward from the disease to a possible exposure • Matching of cases with control is critical • Effect measure: odds ratio 17 Case-control Study
- 18. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Elements 1. Selection of cases: hospital-based/population-based 2. Selection of controls: Same population that gives rise to cases 3. Information on exposure 4. Analysis and interpretation 18 Case-control Study
- 22. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Case-control Study 22 Strengths • Efficient for rare outcomes (diseases and health events) • Cost-effective • Retroactive analysis • Useful for hypothesis generation • Can study multiple exposures Limitations • Selection bias • Recall bias • Limited in establishing temporal relationships • Difficulty in proving causation • Less suitable for rare exposures • Matching issues • Subject to confounding
- 23. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Cohort Study 23 • A group of people with similar characteristics proceeding together in time (birth, age, occupation, etc) • Attempts to study the relationship between a purported exposure or risk factors and the subsequent risk of developing health outcomes • Conceptually longitudinal; the study groups so defined are observed over a period to determine the frequency of disease among them • Begin with disease-free individuals • Classify patients as exposed/unexposed • Record outcomes in both groups Compare outcomes using risk ratio or relative risk (RR)
- 26. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Cohort Study 26 Steps in conducting cohort study • Select suitable study and control cohorts • Data collection and measurement of exposure • Follow-up of cohort and outcome measurement.
- 27. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Cohort Study 27 Risks: Relative Risks and Attributable Risks
- 28. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Cohort Study 28 Strengths • Allows calculation of incidence • Exposure precedes the outcome; clarity of temporal sequence • Examines single exposure but multiple outcomes • Good for investigating rare exposures Limitations • Expensive and time- consuming • Inefficient for rare diseases or diseases with long latency • Attrition or loss to follow-up
- 29. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Experimental Study 29 • Similar in approach to cohort studies, except that the study conditions are under the direct control of the investigator • There is some deliberate action, intervention or manipulation of the exposure • Aim - to provide for the scientific proof of causation - To evaluate new forms of therapy or prevention methods • Can be conducted on animal or humans • Human experiment: - Randomised controlled studies- clinical trials - Field trial - Community trial - Non-randomised
- 30. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Randomised Controlled Clinical Trials 30 • A planned experiment designed to test the efficacy and/or effectiveness of new prophylactic, diagnostic, and therapeutic agents, devices, regimen, services, etc., applied on human subjects • Basically, it involves comparing the outcomes in two groups of individuals 1. Group 1: new treatment or intervention 2. Group 2: standard treatment or control • Types of design include parallel design and cross- over design
- 31. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Randomised Controlled Clinical Trials 31 Steps in conducting an RCT • Appropriate protocol development • Selecting reference and experimental populations • Randomization • Intervention/Manipulation • Follow-up • Assessment
- 32. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Randomised Controlled Clinical Trials 32 Randomization • The heart and soul of the RCT • Ensures that participants have an equal chance of being assigned to one of two or more groups • Participants are allocated into study (new treatment or intervention) and control groups (standard treatment or placebo) on random basis. • It eliminates bias and allows comparability. • Randomization is best done by using table of random numbers.
- 33. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Randomised Controlled Clinical Trials 33 Blinding • Another quality improvement process in RCT • Can be at the level of: - Participants only (single blinding) - Participants and investigator (double blinding) - Partcipants, investigator, and analyst (triple blinding) • Helps eliminate - Co-intervention - Biased outcome ascertainment “Randomized, double-blind, controlled trial” is considered as research design par excellence and “Gold standard” amongst research designs.
- 34. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Randomised Controlled Clinical Trials 34 1. Parallel design 2. Cross-over design
- 35. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Randomised Controlled Clinical Trials 35 Phases in clinical trials
- 36. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Randomised Controlled Clinical Trials 36 Strengths • The only effective method known to control selection bias • Controls confounding bias without adjustment • Maintains advantages of cohort studies Limitations • May be complex and expensive • Lacks representativeness – volunteers differ from population of interest • Ethical challenges are immense
- 37. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Causality 37 • This is central to all of medical sciences • Causation cannot be established without variation of the exposure or risk factors • Randomised trials are not necessarily needed infer causality • You cannot do a randomized trial of everything, due to ethical challenges • Causality can be inferred from other sources
- 38. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Causality 38 Bradford-Hill Criteria for Causality • Direct evidence - Experiment - Strength - Temporal/spatial proximity • Mechanistic evidence - Dose response - Biological plausibility • Parallel evidence - Consistency - Coherence - Analogy • Specificity
- 39. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Summary 39 Objective Study Prevalence Cross-sectional Correlation/Association Cohort and Case-control Odds Case-control Incidence Cohort Prognosis Cohort Natural History of Disease Cohort Treatment effect/strong cause and effect relationship Experimental
- 40. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Systematic reviews and Meta- analysis 40 Systematic reviews aim to comprehensively summarize existing literature on a specific research question using a predefined and transparent methodology. Meta-analysis is a statistical technique used in systematic reviews to quantitatively synthesize data from multiple studies, providing a more robust and precise estimate of the overall effect.
- 41. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Hierarchy of Study designs 41
- 42. Global Health and Infectious Diseases Control Institute – NSUK Public Health Research Methods – GHI 712 Acknowledgements 42 • Health Research Fundamentals by Sanjay Mehendale et. al • Research Methodology for Health Professionals, First ed. by R. C. Goyal • https://www.healthknowledge.org.uk/index.php/pub lic-health-textbook/research-methods/1a- epidemiology/descriptive-studies-ecological-studies • https://www.coursera.org/learn/medical- research/lecture/Tnhkl/causality