Association, Casual inference & causality Flashcards
Cause
An precurser event/condition/characteristic requrired for the occurrence of the diesase
Associations
Does the exposure cause the disease? Associations are relationships btw an exposure and an outcome
3 types of associations
artifactual, non causal, causal
artifactual association
can arise from significant bias or extensive confounding
non causal associations
can occur in 2 ways
- the disease may cause the exposure
- the diesase and the exposure are both associated with a third factor
Koch’s postulate’s(for infectious disease)
4 keys for implicating a causational relationship
- must be present in every case of disease
- must not be found in cases of other disease or healthy individuals
- must be capable of isolation, culture and reproducing disease in experimental animals
- must be recovered from experimentally induced diseased animasl
Koch’s postulate’s limitations
disease production may require presence of co-factors that postulates don’t address
viruses can’t be cultured similar to bacteria
not all viruses bacteria induce clinical diesease
Mill’s Canons
the cuase of any effect must consist of a constellation of components that act in concert
Sufficient cause
a set of minimal conditions/ events that inevitably produce disease. a cuase which preceds a disease, and if present, the diesase will ALWAYS occur
Quite rare apart from genetic abnormailites… homozygous recessive diesase
Component causes
sufficent cause have multipble required components…. a characterisitc that if present and active, increases the probablity of a particular disease …. some patients must be primed or suseptible to disease before component cuases induce disease….
Necessary Cause
a cause which precedes a disease and has the following relationship with it…. cause must be present for the disease to occur, yet the cuase may also be present without the disease occuring… TB
Component cause
in order to examine the influence of a single factor, it is necessary to adjust or control for the effects of the other factors… mathematically or mthodoligically
ways to control for multipple causations
restrictions, matching, stratification
Restricting
keep out the other factors from the study
matching
similar characteristics in each group
stratification
categorize patients on exposure levels or disease severity or other imporatnat patient characteristics
Causal inference process
inductively oriented criteria…. hill’s guidlines. derived foloowing us surgeon generals 1964 report on smoking…. IN what circumstances cna we pass from this observed association to a verdict of causation?
Hill’s Criteria… an interpretive application process
- strength
- consitency… specificity
- temporality
- biologic gradient
- plausibility… coherence, experiment, anaology
The higher the number of criteria met, when evaluating an association, the more likely it may be causal
Strenght
Referes to the size of the association. THe greater the associations, the more convincing it MIGHT actually be causal…
A strong association is neither necessary nor sufficient for causality and weakness of an association is neither necessary nor sufficient for absence of causality.
Consistency
reproducibility… the repeated observation of association in different populations under different circumstaneces in different studies, not just once…. consitency may still obscure the truth…
Temporality
is the necessity that the cause PRECEDE the effect/outcome in the time
Proximate cause
short term interval
distant cause
long term interval
induction period
component cause to diesase onset
latent period
disease onset to diagnosis
Biological gradient
refers to the observation of a gradient of risk (dose-response) associated with the degree of exposure…. some things have a threshhold effect, no effect until a certain level of expsoure is reached
Plausibility(biologically)
refers to the biological feasibility (understanding) the associated can be understood and explained (biologically/physiologically/medically)….. It has to be able to be proven that that can occur in the body for that reason….
Pitfalls in causal research
bias- confounding- effect modifications…..
pitfall synergism
the interaction of 2 or more presumably -causal variables so that the combined effect is clearly greater than the sum of the individual effects
