Introduction to Clinical Epidemiology by 5QUUcj

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									Overview of study
    designs
Reza Majdzadeh,
Professor of Epidemiology
School of Public Health
Tehran University of Medical Sciences
There are two main types of
  epidemiologic studies:




   Intervention
   Observational
Observational studies


  The researchers limit themselves to
  observing the occurrence of disease
  in people who are already segregated
  into different exposure groups.




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There are various types of
observational studies:
  Routine data based studies
    Case report - Case series
    Ecological studies
  Cross sectional
  Case control
  Cohort



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Routine data based studies

   In which the data are derived from routine
   data collection system (e.g. cancer
   registration or death certificates). They
   may be carried out at an individual level if
   information on the exposure(s) of interest
   is available for each of the study subjects
   or at the aggregated level(ecological
   studies) if the group rather than the
   individual is the unit of the study.

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Cross sectional surveys

   In which a sample of subjects from a
   defined population is selected and
   information on the exposure(s), and
   outcome(s) of interest is collected
   simultaneously at a single point in
   time.



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Case control

   A group of patients with a particular
   disease or condition(“cases”) and a
   suitable group of subjects without
   that disease or condition (“controls”)
   are selected and their past exposure
   to putative risk factor is ascertained
   and compared.


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Cohort

   Study population (or cohort) is
   selected and the exposure status of
   its members assessed. The cohort is
   followed up in time and the
   occurrence of disease in the
   different exposure groups is
   measured and compared.


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Intervention studies

   The allocation of the study subjects
   to the different study groups is
   implemented by the investigator.
   Thus, if conducted properly, the
   intervention and the control groups
   would be similar in all respects apart
   from the exposure under study.


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There are two types of
intervention study:
     Clinical trial
     Field trials




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Clinical trials


 Where the main aim is to assess the
 value of new forms of treatment




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Field trials

   Where the objective is to evaluate an
   intervention decreased the risk of
   diseases among disease-free people.
   Field trials can be conducted at an
   individual level, if the unit of
   allocation is individual, or at an
   aggregated level, if the unit is a group
   of people.
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          Observational:
    1. Routine based data studies
    2. Cross sectional
    3. Case control
    4. Cohort




Interventions:
     1. Clinical trial
     2. Field trial

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