1. uses
   1. confirming cause effect association
   2. evaluating various treatment modality
   3. Evaluating feasibility, efficacy & relevance
2. example
   1. experiment by Lind(1753)
      1. 12 pts aboard a ship with scurvy
      2. group into 6, 2 each
      3. given various regime of treatment
      4. 1 group given lemon and orange
      5. After 6 day, sudden improvement observed in group that consume orange and lemon
   2. bypass study group 1985
      1. pts with cerebral ischaemia and obstructed int. carotid artery randomly put into medical and surgery
      2. surgical patient develop sickness earlier than medical team
   3. smoking kills by pearl (1938)
      1. random assignment of smoker to an intensive intervention group or to a control group of "usual" management
      2. lower mortality rate in intervention group provide strong and incontrovertible .....................
3. selection criteria
   1. inclusion
      1. guidelines for proper identification and gradation of cases by the extent and severity of disease to ensure selection of a homogenous study population
   2. exclusion
      1. facilitate omission of patients suffering from atypical disease, any other disease, or disease associated with unusually poor prognosis
4. selection source
   1. clinical trial
      1. randomization -ensure comparability of experimental and control group
   2. risk intervention trial
      1. drawn from high risk population by cluster sampling technique
      2. to avoid operational industries,experimental and control groups should be drawn from identified but separate sources
   3. preventive trials
      1. measure changes in the health picture specific preventive service programme or as a result of package of service encompasing in whole range of health prob
   4. historical trial
      1. patient serve as their own control
      2. compared with their past experience prior to their participation in the trial
5. observation and interaction
   1. consent
      1. obtained after
         1. informing subject the purpose
         2. the procedure
         3. possible outcome of study
         4. so that they able to appreciate advantages and disadvantages assoc. with participation in proposed study
      2. consent given by participant on basis of information provided for them
   2. compliance
      1. ensuring adherence of the subject to the medical advice of the investigator
      2. determine validity of experimental studies
      3. varies among different individual
      4. Individuals who fail to comply are excluded before the trial is formally initiated
      5. several evolved approaches to ensure compliance
         1. counting unused pills, lab estimation of drug or metabolites in blood or urine or addition of safe biochemical markers
   3. end point
      1. outcome event that appear during period of manipulation
      2. positive
         1. return of sense of well being
         2. reduction of severity
         3. arrest of disease
         4. reduction of side effect and complication
      3. negative
         1. comprise and acceleration of disease process
         2. increase its severity
         3. flare up of side effect and complications
         4. deterioration in the patient condition
6. analysis and inference
   1. hospital based
      1. analysis involve periodic assessment of end point
   2. community based
      1. efficacy measured on the basis of disease incidence using attributal risk
7. bias
   1. selection bias
      1. highly selected
      2. inherently biased sample, suffering from a particular grade of a particular disease
   2. observation bias
      1. aware of identity of experimental and control group member
      2. can be eliminated
         1. single blind study
            1. participant
         2. double blind study
            1. participant and investigator
         3. triple blind study
            1. participant, investigator and evaluator
   3. placebo effect
      1. simulate therapeutic agent in color, taste, odor and physical appearance
8. critical estimate
   1. technical
      1. resembles lab experiment in which changes produced in natural phenomena by dints of maneuver
   2. operational
      1. compliance of participants is crucial issue
   3. ethical
      1. based on ethical foundation