outbreaks, causality Flashcards
cohort inclusion is based on-
exposures
case control inclusion is based on-
clinical outcome/disease
attack rate vs secondary attack rate
attack rate #ill/#susceptible
secondary attack rate: #ill/# exposed to primary cases
Using OR to determine source
using case controls, make a 2x2 table for each possible source then calculate OR, high OR = more likely to have been source
simple causality model
cause –> effect
linear causality model
cause –> effect 1/Cause2 –> effect 2
common cause causality model
cause 1 and cause 2 –> effect
common effect causality model
cause –> effect 1 and effect 2
what is the only absolutely essential criterion for causality?
temporality
temporality
cause must precede effect
consistency
same cause always yields same effect
strength
size of risk of cause on effect
specificity
single cause produces specific effects
dose-response relationship
increasing level of exposure to cause will increase risk of effect
biologic plausibility
cause and effect relationship agrees with accepted understanding of biologic processes
coherence
cause and effect relationship is compatible with current knowledge
experiment
cause and effect condition can be altered by appropriate experimental design
necessary and sufficient, example
Cause –> effect
Ex: measles virus is both necessary and sufficient to cause measles in susceptible person
necessary but not sufficient, example
Cause 1 + other cause –> effect
cause 1 is required, but not enough alone to cause effect
ex: mycobacterium tuberculosis is necessary to cause TB infection, but other host factors are also involved
sufficient but not necessary, example
Cause 1 –> effect, cause 2–> effect
other causes yield same effect
Ex: enlarged spleen has many causes
neither necessary nor sufficient
cause 1 may or may not be present and effect can still occur
