Establishing Causality Flashcards
1
Q
Could the association be observed by chance?
A
- if there is less than a 5% chance that the result obtained is due to chance, we accept it as a “real” association, and we can expect to be correct 95% of the time
- there is never a zero percent chance that a result happened by chance
2
Q
Could the association be due to bias?
A
- Bias refers to systematic errors made in data collection
3
Q
Is the relationship due to confounding? - def of Confounding
A
- is the distortion of the association between an exposure and health outcome by an extraneous, third variable
4
Q
To whom does the association apply? (3)
A
- associations are identified using data that is reflective of the population as a whole
- Non-random samples yield results that reflect the characteristics of the sample alone. Small samples cannot be generalized to the entire population with any confidence
- Samples that include a specific subset of the population (women aged 18-25, for example) cannot reliably tell us anything about other subsets of the population
5
Q
Direct Causation
A
- wherein a factor leads directly to the health event of interest
- is characteristic of many infectious diseases, but is atypical of non-infectious illness, except for things like traumatic injury
6
Q
Indirect Causation
A
- a precipitating factor requires the “assistance” of one or more intermediate steps to induce disease
- chronic diseases
7
Q
Necessary
A
- to produce the health outcome in question
- A necessary factor is one that must be present for the disease to occur – like varicella zoster for chicken pox
8
Q
Sufficient
A
- to do so on their own
- A factor is sufficient if its presence is enough to cause the disease
9
Q
Necessary and Sufficient
A
- in the presence of that factor, disease always develops
- without the factor, the disease never develops
- characteristic of some genetic disorders,
10
Q
Necessary but not Sufficient
A
- a factor must be present to cause the disease but is not capable of causing it on its own
- Infectious agents are necessary to induce the diseases attributable to them, but they often need some secondary factor, like a weakened immune system, to take hold and do their thing
11
Q
Sufficient but not Necessary
A
- the factor alone can cause the health outcome, but is not necessary for that outcome to occur
- but so can other factors that are acting alone
- Ex. decapitation
12
Q
Neither Necessary nor Sufficient
A
- a factor cannot, on its own, cause a disease, and it’s not the only thing capable of causing that disease
- one factor alone cannot do it alone
- most common in chronic diseases
13
Q
Temporal Relationship
A
- if a factor is believed to be the cause of a disease, exposure must occur BEFORE the disease develops
- important to consider the length of time that has passed after an exposure (it cannot be too short)
14
Q
Strength of Association
A
- the stronger the association between a health outcome and a potential risk factor, the more likely that it is a causal relationship.
Ex. the relationship between smoking and lung cancer
15
Q
Dose-Response Relationship
A
- if the dose of an exposure increases, the health effects of that exposure will increase
Ex. more cigarettes you smoke, the more likely you are to develop a variety of cancers - there is a threshold dose beyond which the effects can get no worse
Ex. to kill someone with arsenic, there is a threshold to its toxicity
16
Q
Evidence for a Causal Relationship (3)
A
- organism is always found with the disease
- organism is not found with any other disease
- organism , who isolated from one who has the disease and cultured through several generations, produces the disease (in experimental animals)
17
Q
Replications of the Findings
A
- has to be found consistently in different studies and in different populations
- if findings can’t be replicated, then the association is likely due to chance
18
Q
Biological Plausibility
A
- must not violate what we understand about biology
19
Q
Consideration of Alternative Explanations
A
- always consider the role of confounders
20
Q
Cessation of Exposure
A
- If an exposure is causal, it’s quite reasonable to assume that elimination of the exposure will reduce the incidence of the disease
21
Q
Consistency with Other Knowledge
A
- to not being in opposition to what other sources of information are telling us
22
Q
Specificity of the Association
A
- one exposure should cause one disease
- but this is not common
