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Study Design

Study Design. Lecturer: Leonardo Tamariz, MD, MPH Division of Medicine University of Miami. Required Reading. Schulz KF, Grimes DA. Case-control studies: research in reverse. Lancet. 2002 Feb 2;359(9304):431-4.PMID: 11844534

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Study Design

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  1. Study Design Lecturer: Leonardo Tamariz, MD, MPH Division of Medicine University of Miami

  2. Required Reading • Schulz KF, Grimes DA. Case-control studies: research in reverse. Lancet. 2002 Feb 2;359(9304):431-4.PMID: 11844534 • Grimes DA, Schulz KF. Cohort studies: marching towards outcomes. Lancet. 2002 Jan 26;359(9303):341-5.PMID: 11830217

  3. Objectives Be able to: Define the following measures of morbidity (prevalence and incidence) Identify factors that affect the measures of morbidity. Describe the key characteristics of each type of study design, specifically: Differences between observational and experimental designs Direction of association between exposure and outcomes Advantages and disadvantages

  4. Definitions: Measures of Morbidity Prevalence Incidence

  5. Prevalence # of ALL cases of a disease present in a population at a single point in time Prevalence = ------------------------------------ # people at risk for the disease at a single point in time

  6. Incidence # of NEW cases of a disease occurring in the population during a specified period of time Incidence = ------------------------------------ # of people at risk of developing the disease during a period of time

  7. Review

  8. Factors that affect Measures of Morbidity

  9. Factors that affect Prevalence Incidence (higher incidence increases prevalence) Death and Cure (Decrease prevalence) Prevalence

  10. Study Design

  11. Research Cohort Case-control Cross sectional Observational Quantitative Experimental Randomized trials • Observational studies: An investigator does not intervene • in the study subjects. • Experimental studies: An investigator assigns (intervenes) • interventions to the study subjects.

  12. Cohort: Direction of the Association Exposure Outcome Pancreatic cancer Coffee Time

  13. Types of Cohort Past Present Future Retrospective Prospective Non-concurrent Concurrent

  14. Question • You are planning a cohort study to see if CRP (exposure) is associated with myocardial infarction (outcome). In planning you are not sure if you should use a retrospective or prospective design?

  15. Advantages • Advantages of the Retrospective Design • Easy to do (look at medical records) • Inexpensive • Get results quickly

  16. Disadvantages • Disadvantages of the Retrospective Design • Relying on medical records • The patients who got tested for CRP probably have a higher risk of the outcome (MI) than those who did not get tested (BIAS)

  17. Prospective Design • What are the advantages and disadvantages of the Prospective Design?

  18. Advantages • Advantages of the prospective design • You can standardize how you collect the data • Everyone gets the test (CRP)

  19. Disadvantages • Disadvantages of the prospective design • Expensive • You have to wait 5 years for the results

  20. Cohort Studies Advantages Best way to ascertain the natural history of a disease (prognosis) Investigate multiple outcomes. Can calculate risk Disadvantages Expensive (prospective) Cannot evaluate rare diseases Selection bias Loss to follow up Need to adjust for confounders

  21. Case-control: Direction of the Association OutcomeExposure Cases: Participants with the outcome Controls: Participants without the outcome Exposure

  22. Case Control Studies Advantages Most efficient design in terms of time, money and effort. Can be used for rare diseases or harm questions. Disadvantages No temporality Time is not taken into account Built in bias Recall bias Can not calculate risk

  23. Cross-sectional: Direction of the Association Exposure: Smoking In cross-sectional studies the exposure and outcome are assessed at the same time Outcome: Prevalence of lung cancer

  24. Cross-sectional: Disadvantages Exposure: Smoking Arthritis 50 pack Year Smoker Cannot asses prior changes in the exposure ? No directionality Which one came first Decides to quit Outcome: Prevalence of lung cancer Obesity 24

  25. Randomized Clinical Trials (RCT) yes yes Outcome no Intervention yes no Outcome no

  26. End of Lecture • If you have any questions regarding this lecture feel free to contact me at ltamariz@med.miami.edu

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