Week 14: Common Research Designs and Issues in Epidemiology

• Study Designs

  • According to objective
  • According to temporal sequence
  • According to manipulation of variables
• According to Objective

  Descriptive

  • Case Report
  • Case Series
  • Ecologic Studies

  Analytical

  • Case-Control Studies
  • Cohort Studies
  • Experimental Studies
• According to Temporal Sequence

  Longitudinal

  • Prospective
  • Retrospective

  Cross Sectional
• According to manipulation of variables

  Experimental

  • Clinical Trial
  • Community Trial

  Observational

  • Cross sectional Studies
  • Case control Studies
  • Cohort Studies
• Cohort Studies

  • single exposure, multiple outcome

  Classification

  • analytic
  • observational
  • longitudinal (E—D)

  Objective

  • to show that the probability of disease is greater in exposed than the unexposed

  Study Population

  • exposed
  • unexposed
• Cohort Studies

  Used to;

  • indentify the risk or rate, protective or prognostic factors
  • describe the natural history of disease
  • predict the number of new cases in a population over time
• Cohort - specific characteristic of group of people

  • In cohort studies, group are defined on the basis of exposure and are followed for outcomes
• Prospective Cohort Studies - moving forward

  Advantages

  • investigator can control and standardize data collection and can check the outcome of events
  • estimates of risk represent true risks for groups being studies (absolute risk)
  • can look at multiple effects from a single exposure

  Disadvantages

  • only risk factors defined at the beginning of the study can be used
  • higher researcher cost
  • participant drop outs
  • requires long follow up
• Retrospective Cohort Studies - moving backward

  • in this approach the investigator uses historical data to define a risk group and follows group members up to the represent to see what outcome have occured

  Advantages

  • similar to prospective cohort studies
  • time and cost limitations can be minimized

  Disadvantages

  • lacks the ability to monitor (already happen) and control data collection
• Case-Control Studies

  • multiple exposure, single outcome

  Classification

  • analytic
  • observational
  • retrospective

  Objective

  • to show the probability of exposure is greater in those with disease

  Study Population

  • Case Group (with disease)
  • Control Group (without disease)
• Case-Control Studies

  Used to ;

  • identify possible causes of disease
  • quantify sensitivity and specificity
• Case-Control Studies

  • the investigator selects the case group and the control group on the basis of a defined outcome
  • compares the group of their frequency of past exposyre to possible risk factors
  • can estimate the relative risk of the outcome (odds ratio)
• Case-Control Studies

  Advantage

  • requires small number of subjects for study
  • inexpensive
  • desirable when the disease occurence is rare

  Disadvantage

  • recall bias
  • temporal relationship may be difficult to establish
  • information on potential risk factors and confounders may not be available
• Case-Control Studies

  Sources of Cases

  • cohort study
  • hospital
  • population
  • disease registries
  • occupational groups
  • insurance companies
• Commonly Used Controls

  • probability of samples of population from source populayion which gave rise to cases
  • patients from same institution with unrelated conditions
  • neighbors
  • friends, associates, siblings
• Nested Case-Control Studies

  • the disease should be manifested first before you can choose the control and experiment group

  Case-Cohort Study

  • even without disease manifestation, you can pick the control and experimental group