Final: Lecture 19 Flashcards
Associations (3 main types)
- Are relationships between an exposure and an outcome
- Artifactual (a.k.a. False) can arise from significant bias and/or extensive confounding, accidental, worst kind we don’t want!
- Non-causal
- Causal
Any precursor event/condition/characteristic required for the occurrence of the disease is _______.
•Cause
Non-causal Associations (2 ways)
- The disease may CAUSE the exposure (rather than the other way around) Ex. RA leading to physical inactivity
- The disease and the exposure are both ass. with a third factor (confounding)
•Coffee drinking and CHD, or Down’s syndrome and birth order
Koch’s Postulate’s (for infectious disease)
•4 key postulates for implicating a causal 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 animals
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 disease, carrier and sub-clinical disease
The cause of any effect must consist of a constellation of components that act in concert is know as ________.
•Mill’s Canons: have to have everything prime and set to cause disease
Sufficient Cause
- A set of minimal conditions/events that inevitably produce disease
- A cause which precedes a disease, and if present, the disease will always occur
- Rare, apart from genetic abnormalities
- Have multiple, required “components” (termed Component Causes (a.k.a. Risk Factors) that collectively act to 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 cause may also be present without the disease occurring
Component Cause (a.k.a. Risk Factor)
- A characteristic that, if present and active, increases the probability of a particular disease
- Ex. High LDL levels are RF for heart attacks, but not all persons with high LDL suffer from heart attacks
- Some patients are “primed” or “susceptible” to disease
- By themselves not enough to cause disease
3 ways to control/adjust for other factors/characteristics (multiple causation)
- Restriction: (keep out the other factors from study) Ex only include patients ≥65 years of age or don’t allow smokers
- Matching: (similar characteristics in each group) Ex. match age, gender, disease severity, smoking status ect.
- Stratification: Categorize patients on exposure levels or disease severity, or other important patient characteristics
Inductively-oriented criteria are used:
- Hill’s Guidelines are used
- “In what circumstances can we pass from the Observed association to a verdict of causation?”
- Hill disagreed that “hard-and-fast” rules of evidence could be generated by which to judge likelihood of causation
Hill’s Guidelines**
•Causal Inference Process, an interpretive, application process
- Strength
- Consistency
- Temporality
- Biologic Gradient
- Plausibility
•The higher the number of criteria met, when evaluating an association, the more likely it may be the causal.
Strength
- Refers to size of the ass.
- Greater the ass. the more convincing it is that the ass. might acutally be causal
- A strong ass. is neither necessary nor sufficient for causality and weakness of ass. is neither necessary nor sufficient for absence of causality**
Consistency (a.k.a. Reproducibility)
- The repeated observation of ass. in different populations under different circumstances in different studies (not just once!)
- Consistency may still obscure the truth! **
Temporality*
- Is necessity that the cause precede the effect/outcome in time
- Time-order also describable: proximate cause (short time interval) Distant cause (long term interval)
- Did symptoms start an hour after taking or 8 years? you can have an allergic reaction even after the 5th time taking it
