3. COHORT & CASE CONTROL

3. COHORT & CASE CONTROL

1. COHORT STUDIES

   • cohort: group of persons sharing a common characteristic (geogr, occup, sex, race,etc).
     • 1. SOURCE POPULATION:se sacan entire or random sample, se descartan enfermos YA con outcome (exposure always preceed outcome) but sometimes disease IS the exposure y se evaluan muertes
       • 2.FOLLOW OVER TIME for new events, calculating eg. risk v rate
         • useful for studying uncommon or rare exposures
   • measure incident cases -- can be PROSPECTIVE OR RETROSP., OPEN or CLOSE

2. CASE CONTROL STUDIES

   • for studying rare diseases(<10%). Is INDUCTIVE (from effect to cause, RETROSPECTIVE)--can really MIRROR a cohort
     • 1. Define&select CASES (sick people)
     • 2. Define&select CONTROLS (nonsick): restricted source population from which cases arise
       • MATCHING: for every case, one control has the same variable--should be only STRONG factors
     • 3. Measure&compare EXPOSURE PREVALENCE
       • CANNOT use rate&risk, ONLY ODDS (the control is not representative of the population

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