Common research designs and issues

• Study designs

  • according to objective
  • temporal sequence
  • manipulation of variables
• According to objectives

  Descriptive

  • Case report
  • ass series
  • ecologic studies

  Analytical

  • case control studies
  • cohort studies
  • experimental
• 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
• Classification of Cohort

  • analyticl
  • observational
  • longitudinal
• Objective of cohort

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

  used to identify risk or rate, protective or prognostic factors

  describe natural history of a disease

  predict number of new case in a population over time
• Case control studies

  • analytical, observational, and retrospe
  • to show that the probability of exposure is hreater in those with disease
  • ised to identify possible cause of disease
  • quantify sensitivity and specificity of screening, diagnostic or lab test in the indentifying cases of a disease
  • compares the groups in terms of their frequency of past exposure to possible risk factors
  • estimate the relative risk of the outcome (odds ratio)
• Nested case control

  • baseline characteristics if the participants are obtained by interview, physical examination, and pertinent lab
  • Then follow up to determine the outcome
  • condition of interest developed vs. who did not develop condition of interest
• Case cohort study

  • begins with cohort study, the controls are similarly drawn from the cohort study but are identified before any cases develop
  • Analysis is more complex than other case of control studies