CAUSAL INFERENCE. Dr. A. K. AVASARALA MBBS, M.D. PROFESSOR & HEAD DEPT OF COMMUNITY MEDICINE & EPIDEMIOLOGY PRATHIMA INSTITUTE OF MEDICAL SCIENCES, KARIMNAGAR, A.P. INDIA : +91505417 [email protected] CAUSAL INFERENCE.
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IT IS A TRIAL PROCESS AS NO EPIDEMIOLOGICAL EXPERIMENT, EVEN EXPERIMENTAL ONES, CAN PROVE OR ESTABLISH CAUSE-EFFECT RELATION SHIP CENT PER CENT.
THIS CAUSAL ASSOCIATION CAN BE NEITHER PROVED NOR ESTABLISHED CENT PER CENT..ONLY THE MAXIMUM EXTENT OF PROBABILITY OF THEIR INTER-RELATIONSHIP CAN BE EXPLAINED..
BY WEEDING OUT OR EXCLUDING VARIOUS FALSE LINKS AND REACHING THE REAL LINK
THIS PROCESS HAS TO BE DONE WITHOUT ANY ERRORS, EITHER SYSTEMATIC (BIASES) OR DUE TO CHANCE.
KARL POPPER -- REFUTATIONIST
KUHN, LAKTOS-- REJECTEDKARL
PHILOSOPHERS & SCIENTIST JUDGEMENT
AGREEMENT: IF A FACTOR IS COMMON TO A NUMBER OF DIFFERENT CIRCUMSTANCES, THAT ARE ASSOCIATED WITH THE PRESENCE OF A DISEASE, THAT FACTOR MAY BE THE CAUSE OF DISEASE – THAT MEANS THERE IS AN AGREEMENT BETWEEN THE FACTOR AND THE DISEASE UNDER DIFFERENT CIRCUMSTANCES.
DIFFERENCE: IF THE FREQUENCY OF A DISEASE IS MARKEDLY DIFFERENT UNDER TWO DIFFERENT CIRCUMSTANCES AND SOME FACTORS CAN BE IDENTIFIED IN ONE CIRCUMSTANCE NOT IN OTHER, THEN THE FACTOR OR ITS ABSENCE, MAY BE THE CAUSE OF DISEASE.
CONCOMITANT VARIATION: FACTOR WHOSE FREQUENCY OR STRENGTH VARIES WITH THAT OF THE DISEASE, IT MAY BE THE CAUSE OF THE DISEASE.
POPPER BELIEVED THAT SCIENTIFIC STATEMENTS CAN NEVER BE PROVED OR ESTABLISHED AS TRUE LOGICALLY AND SCIENCE ADVANCES BY A PROCESS OF ELIMINATION CALLED CONJECTURE(GUESS) AND REFUTATION(DENIAL OR PROVING AS WRONG)
MILLS & BACON INDUCTIVISM
REJECTED BY DEDUCTIVISTS, DAVID HUME THAT INDUCTIVISM LACK LOGIC
REJECTED BY KARL POPPER BY THEORY OF FALSIFICATION
SCIENTIFIC LAWS & FACTS ARE NOT KNOWN WITH CERTAININTY AND DEDUCTIVE LOGIC YEILDS CONCLUSION ONLY WHERE THEY ARE 100% CERTAIN
SCINTISTS JUDGEMENT REGARDING CASUALITY IS BETTER – SUSSER& BAYES
FALSIFICATION THOERY WAS REJECTED BY SUSSSER & KUHN AS IT IS PESSIMISTIC
It is an event, condition or characteristic, that precedes the disease event and without which the disease event wouldn’t have occurred at all or until later date
What is necessary cause?
It is the principal cause in all causal constellations with out which the disease cannot occur even though other causes are presented and operating
The causes other than necessary cause, complementing or helping the necessary cause are considered as components of the cause.
These are set of causes necessary to make a factor sufficient to cause the disease . They just complement each other and act as independent partners. They will not loose their individual identity, there is no change in their biological mechanisms.
Is entire set of factors or conditions and each component complement each other for causal co-action or joint action.
It is a set of minimal (all necessary conditions and events) conditions and events that inevitably produce the disease. Sufficient cause competes causal mechanism and initiates the disease
A= NECESSARY CAUSE ABCDE= CAUSAL COMPLEMENT
MYCO TB (A)
A: NECESSARY CAUSE
SMOKING (A) UNFILTERED CIGARETTES (B) 16YR DURATION (C) HOST SUSCEPTABILITY(D)
A: NECESSARY CAUSE
COULD IT BE SELECTION OR MEASUREMENT BIAS
COULD IT BE DUE TO CONFOUNDING
COULD IT BE DUE TO CHANCE
COULD IT BE CAUSAL?
APPLY CHECK LIST AND MAKE JUDGMENT
(COURTESY: BASIC EPIDEMIOLOGY BY BEAGLEHOLE & KNOLL)
Book of Public Health
principles & methods