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Study Design

Study Design. DR. KHALED ALDOSSARI SBFM , ABFM ,MBBS ASS. PROFESSOR , FAMILY MEDICINE SAU. Learning Objectives. To understand the concepts of different study designs To learn about the advantages and disadvantages of several study designs. Performance Objectives .

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Study Design

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  1. Study Design DR. KHALED ALDOSSARI SBFM , ABFM ,MBBS ASS. PROFESSOR , FAMILY MEDICINE SAU Adapted from work of Jozeoh and Colin MC,Gary Clark, keith MD and dr.Sonita Dondani ppt

  2. Learning Objectives • To understand the concepts of different study designs • To learn about the advantages and disadvantages of several study designs

  3. Performance Objectives After this lecture the student will be able • To recognize concepts of different study designs • To appropriately use a study design in research projects

  4. Epidemiologic study designs The basis for the lecture is the distinction between descriptive epidemiology and analytic epidemiology Descriptive epidemiology: seeks to measure the frequency in which diseases occur or collect descriptive data on possible causal factors. Analytic epidemiology: attempts to specify in more detail the causes of a particular disease”

  5. Epidemiologic study designs Types of Epidemiologic Observational Studies based on: • type of sampling from population - based on Exposure &/or Disease or neither • temporal sequence of observation - one time point, forward, backwards

  6. Descriptive Studies • Case reports • Case series • Population studies

  7. Descriptive Studies: Uses • Hypothesis generating • Suggesting associations

  8. Epidemiologic study designs Study designs Case series • Case Series report new diseases or health related problems. • They may provide some descriptive data on exposures to potential causal factors

  9. Analytical Studies • Experimental

  10. Observational Studies • Cross-sectional • Case-control • Cohort

  11. Cross-sectional Study • Data collected at a single point in time • Describes associations • Prevalence A “Snapshot”

  12. Prevalence vs. Incidence • Prevalence • The total number of cases at a point in time • Includes both new and old cases • Incidence • The number of new cases over time

  13. Example of a Cross-Sectional Study Association between garlic consumption and CAD ( coronary artery disease ) in the Family Practice Clinic

  14. Cross-sectional Study Sample of Population Garlic Eaters Non-Garlic Eaters Prevalence of CAD Prevalence of CAD Time Frame = Present

  15. Cross-sectional Study Garlic Consumption - + 10 90 CAD + 90 10 -

  16. Epidemiologic study designs Cross-sectional studies • Cross-Sectional Studies measure existing disease and current exposure levels. • They provide some indication of the relationship between the disease and exposure or non-exposure

  17. Epidemiologic study designs Cross Sectional Studies(contd) • sample without knowledge of Exposure or Disease • sample at one point in time • Mostly prevalence studies/surveys

  18. Epidemiologic study designs Cross Sectional Studies(contd) Advantages • Good design for hypothesis generation • Can estimate overall and specific disease prevalence and sometimes rates • Can estimate exposure proportions in the population • Can study multiple exposures or multiple outcomes or diseases

  19. Epidemiologic study designs Cross Sectional Studies(contd) Advantages • Relatively easy, quick and inexpensive • No issue of subjecting any animals or producers to particular treatments • Best suited to studying permanent factors (breed, sex, blood-type) • Often good first step for new study issue

  20. Epidemiologic study designs Cross Sectional Studies Disadvantages • Problems with temporal sequence of data • hard to decide when disease was actually acquired • disease may cure the exposure • miss diseases still in latent period • recall of previous exposure may be faulty

  21. Epidemiologic study designs Case-control studies • Case-Control Studies identify existing disease/s and look back in previous years to identify previous exposures to causal factors. • Cases are those who have a disease. • Controls are those without a disease. • Analyses examine if exposure levels are different between the groups.

  22. Observational Studies Case-Control Study • Start with people who have disease • Match them with controls that do not • Look back and assess exposures

  23. Case-Control Study Cases High Garlic Diet Patients with CAD Low Garlic Diet Controls High Garlic Diet Patients w/o CAD Low Garlic Diet Past Present

  24. Example of a Case-Control Study Are those with CAD less likely to have consumed garlic?

  25. Case-Control Studies: Strengths • Good for rare outcomes: cancer • Can examine many exposures • Useful to generate hypothesis • Fast • Cheap • Provides Odds Ratio

  26. Case-Control Studies: Weaknesses • Cannot measure • Incidence • Prevalence • Relative Risk • Can only study one outcome • High susceptibility to bias

  27. Cohort Study • Begin with disease-free patients • Classify patients as exposed/unexposed • Record outcomes in both groups • Compare outcomes using relative risk

  28. Prospective Cohort Study CAD Garlic Free No CAD CAD Garlic Eaters No CAD Present Future

  29. Example of a Cohort Study To see the effects of garlic use on CAD mortality in a population

  30. Cohort Study: Strengths • Provides incidence data • Establishes time sequence for causality • Eliminates recall bias • Allows for accurate measurement of exposure variables

  31. Cohort Study: Strengths • Can measure multiple outcomes • Can adjust for confounding variables • Can calculate relative risk

  32. Cohort Study: Weaknesses • Expensive • Time consuming • Cannot study rare outcomes • Confounding variables

  33. Cohort Study: Weaknesses • Exposure may change over time • Disease may have a long pre-clinical phase • Attrition of study population

  34. Experimental Studies Clinical trials provide the “gold standard” of determining the relationship between garlic and cardiovascular disease prevention.

  35. Clinical Trials • Randomized • Double-blind • Placebo-controlled

  36. Clinical Trial R a n d om i z e Treatment Group Outcomes Study Population Outcomes Control Group

  37. Clinical Trial Randomi ze No CAD Garlic Pill CAD Study Population No CAD Placebo CAD

  38. Clinical Trials Strengths: • Best measure of causal relationship • Best design for controlling bias • Can measure multiple outcomes Weaknesses: • High cost • Ethical issues may be a problem • Compliance

  39. Epidemiologic study designs What type of study to chose depends on: • what is the research question/ objective • Time available for study • Resources available for the study • Common/rare disease or production problem • Type of outcome of interest • Quality of data from various sources • Often there are multiple approaches which will all work • Choosing an established design gives you a huge head start in design, analysis and eliminating biases

  40. CLINICAL QUESTIONS, TYPES OF QUESTIONS AND PICO Patrick O’Connor - Toowoomba Clinical Library Service QULOC Seminar Evidence-Based Practice in Health for Librarians University of Queensland 1 September 2010

  41. Outline • Types of questions • Background • Foreground • Question domains • Breaking down clinical scenarios • Keywords • PICO(t)

  42. Steps in the EBP • Formulate an answerable question • Determine the type of question (therapy, dx, prognosis) • Identify the ideal study design for your question • Systematically search the literature to find the best available evidence

  43. PICO(t) • Population / patient / procedure • Intervention / interest / indication / instrument • Comparison • Outcome • type of study design

  44. PICO • Works best with therapy domain. In children with appendicitis (P) does a keyhole approach (I) compared to laparotomy (C) lead to reduced complications (O)?

  45. PICO – dx • Works with diagnostic domain questions. “Is neck stiffness pathognomonic for meningitis?” You can easily extract the Patient (“Child with sepsis”), Interest (“Neck stiffness”) and Outcome (“Meningitis”).

  46. PICO - aetiology, prognosis • Works with aetiology (risk) / prognosis domain questions. In neonates (P) who have developed Intra-uterine Growth retardation (I) what is the risk of developmental delay at 2 yrs of age (O)? In infants (P) who receive a head injury (I) what is the subsequent risk of ADHD (O)?

  47. Preparing your PICO • Select your keywords and their synonyms • Clarify acronyms (BSE, EBM…) • Check your spelling • Check colloquialisms (middle ear infection, glue ear, OM, AOM…) • Terminology / subject headings • Types of study design • Databases / resources to use

  48. PICO – structure your question

  49. Question type – Study design – search tip

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