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Chapter 3

Chapter 3. Overview of Epidemiologic Study Designs. Learning Objectives. Name the elements of a study design (HUIT – H ypothesis tested or not, U nit of observation, I ntervention, T iming of exposure and outcome measures) Link study designs to appropriate research goals

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Chapter 3

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  1. Chapter 3 Overview of Epidemiologic Study Designs

  2. Learning Objectives • Name the elements of a study design (HUIT – Hypothesis tested or not, Unit of observation, Intervention, Timing of exposure and outcome measures) • Link study designs to appropriate research goals • Distinguish between study designs in terms of how the HUIT elements are treated • Determine the appropriate use of each study design

  3. Study Designs • Review common designs used in epidemiologic research • Research question should influence the choice of design • Choices may also be limited by the availability of resources • Need to balance between methodological rigor and practicality • Sometimes the research question must be adjusted accordingly

  4. HUIT Elements • H: a hypothesis is tested or not • U: unit of analysis (individual or group) • I: an intervention or treatment is evaluated or not • T: temporal ordering of the time of measuring the exposure and the outcome (disease or death)

  5. Case Report and Case Series • H: no hypothesis tested • U: unit of analysis is the individual • I: no intervention • T: temporal order is not relevant because there is not hypothesized exposure • Defining characteristic: small number of subjects (one or a few) • Strengths: examine new diseases, easy, generate hypotheses • Weakness: no control group for comparison,can’t address specific questions

  6. Example: HIV/AIDS Research • The earliest information about what we now know as AIDS/HIV was learned from case studies and case series of patients (1981) • Common characteristics of these patients were that they were male, young, otherwise healthy, and homosexual • Stimulated hypothesis that the mysterious diseases were somehow transmitted through homosexual contact

  7. Ecological Study • H: hypothesis is tested • U: unit of analysis is the group • I: no intervention tested • T: exposure and outcome measured at the same time • Defining characteristic: group as the unit of analysis • Strengths: can use data already collected; can consider social or group influences • Weaknesses: imprecise measures of exposure and outcome; ecologic fallacy

  8. Ecologic Fallacy • Mistaken interpretation of study results of group-level data to the individual level • Fallacy was first noted in the work of Emile Durkheim, 19th century social thinker • Found that predominantly protestant European counties had higher suicide rated compared to predominantly catholic countries • Mistake: cannot assume that the individuals who commit suicide are protestant and not catholic

  9. Example: HIV/AIDS Research • An ecological study of ethnicity and HIV prevalence found that American nations with higher proportions of immigrants from Africa, Asia, and Europe also had higher prevalences of HIV (Pepin, 2005)

  10. Cross-Section Study • H: hypothesis is tested • U: unit of analysis is the individual • I: no intervention tested • T: exposure and outcome are measured at the same time • Defining characteristic: simultaneous measurement of the exposure and outcome • Advantages: can measure prevalence; time and cost efficient • Disadvantages: cannot establish causality because cannot prove exposure comes before outcome in time; inefficient for rare outcomes

  11. Example: HIV/AIDS Research • Study of injection drug users in Madrid, Spain (Bravo Portella et al., 1996) • Risk factors for self-reported HIV seropositivity included • Passing and taking used syringes • Inconsistent condom use with different types of partners • Variety of types of drugs used • History of incarceration • Can only assume risk factor preceded infection

  12. Case-Control Study • H: hypothesis is tested • U: unit of analysis is the individual • I: no intervention is tested • T: the outcome is measured before the exposure in study time • Defining characteristic: two separate groups are identified for data collection—people with the outcome (cases) and people without (controls) • Advantages: efficient for rare outcomes • Disadvantages: potential for misclassification bias; cannot measure incidence or prevalence

  13. Example: HIV/AIDS Research • Study of Belgian men who had lived in Africa (Bonneauxet al., 1988) • 33 men with HIV and 119 men without HIV • HIV positive men were more likely than HIV negative men to have had: • Sexual contact with local women in Africa (OR = 14.7) • Sexual contact with prostitutes (OR = 10.8) • Medically-prescribed injections by unqualified medical staff (OR = 13.5)

  14. Cohort Study • H: hypothesis is tested • U: unit of analysis is the individual • I: no intervention is tested • T: exposure is measured before (prospective) or after (retrospective) the outcome in study time • Defining characteristic: subjects are followed over time either forward in real time or backward in historical time • Advantages: can measure incidence; can demonstrate temporal order of exposure and outcome; efficient for rare exposures • Disadvantages: can be very expensive and time-intensive;potential for bias due to high attrition (loss of subjects over time); inefficient for rare outcomes and phenomena with long latency periods

  15. Example: HIV/AIDS Research • Cohort of homosexual men followed from 1982 to 1983 (Goedert et al., 1984) • Incidence of HIV infection was 1.2% per month • The greater the number of partners and incidents of receptive anal intercourse, the higher the incidence of infection

  16. Community Trial • H: hypothesis is tested • U: unit of analysis is a group (e.g., community) • I: intervention is tested • T: exposure occurs (and is measured) before the outcome • Defining characteristic: experimental design with a group as the unit of analysis • Advantages: can demonstrate causality, potential to minimize bias and confounding • Disadvantages: expensive and time-intensive; ecologic fallacy

  17. Example: HIV/AIDS Research • Analysis of HIV prevention trials using communities or treatment facilities as the unit of analysis (Wilkinson and Rutherford, 2001) • Found modest increases in condom use with casual partners • Very little or no reductions in HIV and STI (sexually transmitted infections) incidence

  18. Experimental/Clinical Trial • H: hypothesis is tested • U: unit of analysis is the individual • I: intervention is tested • T: exposure occurs (and is measured) before the outcome • Defining characteristic: experimental design, ideally with pre-test, post-test, randomization, and a control group • Advantages: can demonstrate causality, potential to minimize bias and confounding • Disadvantages: expensive and time-intensive; limited external validity (represents the intended target population); subject to attrition bias

  19. Summary of Designs • E=exposure; O=outcome

  20. Hybrid Designs • Combines elements of 2 or more designs in one study • Nested case-control is a common design • Identify cases and controls within a cohort study • Multi-level designs • Uses both individual- and group-level units in the same study

  21. Example: HIV/AIDS Research • Group- and individual-level data were analyzed to learn more about HIV risk in African communities (Uchudi et al., 2011) Group Level Individual Level PermissiveSexual Norms Multiple Sex Partners Tolerance of Polygamy

  22. Designs and Research Goals

  23. Choosing a Design Study Question Study Resources Methodological Rigor Study Design

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