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Study Design

Delve into different study designs in family medicine to grasp advantages and disadvantages for research. Understand descriptive and analytic epidemiology, and explore observational studies like case-control and cohort. Gain insights into cross-sectional studies and their significance in hypothesis generation while navigating through strengths and limitations. Adapted from the works of prominent experts in the field, this lecture aims to enhance your knowledge on the fundamental principles of epidemiologic study designs.

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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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