Module 15

Question 1

What are the nine criteria for assessing causality, according to Bradford Hill?

Answer 1

1. Temporality or time sequence
2. Consistency or repetition across studies
3. Biological or social plausibility
4. Strength of association
5. Dose response or biological gradient
6. Specificity
7. Coherence
8. Experimental evidence
9. Analogy

Question 2

How to decide if an exposure is causal

Answer 2

The general question:
-Is there a cause and effect relationship between the presence of factor X and the development of disease Y?
The answer:
-is made by inference and relies on a summary of all valid evidence

Question 3

What are the five most important Bradford Hill criteria?

Answer 3

Temporality
Consistency across studies
Biological or sociological plausibility
Strength of association
Dose response (or biological gradient)

Question 4

Temporality

Answer 4

In order for an exposure to cause a dz, the exposure must precede the dz in time

Question 5

Consistency of association or repetition across studies

Answer 5

The same results are replicated by different investigators in different settings with different methods. They are repeatedly observed in different places and times.

Question 6

Biological credibility, biological plausibility, or sociological possibility

Answer 6

Is there a logical causal pathway by which this exposure could cause the outcome? Is the association biologically supported? Or sociologically, if social factors are being studied?
But suppose the exposure is only causal under certain conditions or in certain populations but not others?

Question 7

Strength of association

Answer 7

The point estimate or measure of association between the exposure and dz is strong
But is the state of our knowledge always sufficient to identify a causal pathway?

Question 8

Dose-dependent relationship of biological gradient

Answer 8

An increasing amount of exposure is associated with the risk of dz in an increasing or decreasing pattern
But do some exposures have thresholds?

Question 9

Judgment

Answer 9

Once a statistical association is deemed valid, then the totality of the evidence needs to be considered before making a judgment about whether causality exists for a specified hypothesis

Question 10

Health related states or events typically have a ______ etiology

Answer 10

Multi-factorial

Question 11

Combinations of necessary/sufficient causes

Answer 11

Necessary and sufficient
Necessary but not sufficient
Sufficient but not necessary
Neither sufficient nor necessary

Question 12

Necessary and sufficient

Answer 12

The factor always causes dz and is enough to cause the dz alone
Very few causes are necessary and sufficient

Question 13

Necessary but not sufficient

Answer 13

The factor MUST be present to cause the dz, but other factors are also required

Question 14

Sufficient but not necessary

Answer 14

The factors, when present always causes the dz, but there are other ways of getting the dz without the factor

Question 15

Neither sufficient nor necessary

Answer 15

The factor is a contributing cause to the dz but is not always present in all cases of the dz and cannot cause the dz alone
Most risk and protective factors are this type

Question 16

Necessary and Sufficient Causes and causal pies

Answer 16

Component cause (piece of the pie)
Sufficient cause (the whole pie)
Necessary cause (an always present piece of pie)

Question 17

Component cause

Answer 17

Any one of a set of conditions which are part of the sufficient cause

Question 18

Sufficient cause

Answer 18

The whole group of component causes together, which inevitable leads to the dz

Question 19

Necessary cause

Answer 19

A component cause that is part of every sufficient cause

Question 20

3 steps to evaluating study results

Answer 20

1. Consider the role of chance
   -Statistical significance
2. Consider the role of bias
   -Selection bias
   -Information bias
   -Confounding
3. Consider criteria for causality
   -Sir Austin Bradford Hill’s 5 most important criteria

Question 21

Koch’s postulates for infectious dz

Answer 21

To be considered a CAUSE of a dz a microorganism:
-Should be found in all pts with the dz
-Should be grown in vitro (in a suitable medium)
-Should be capable of reproducing the dz in some animal species
-Should be then recovered and grown again in a pure culture

Question 22

Example of temporality, time sequence

Answer 22

HTN precedes a stroke in time

Question 23

Example of consistency of association or repetition across studies

Answer 23

Many different studies in many parts of the world have shown an association between low SES and mortality…not just one study…not just one group of ppl

Question 24

Example of biological credibility, biological plausibility, or sociological plausibility

Answer 24

Gambling may be statistically associated with cirrhosis of the liver, but is it biologically plausible? Excessive alcohol consumption is also associated with cirrhosis of the liver, and is biologically credible, since the liver processes the alcohol

Question 25

Example of strength of association

Answer 25

In some studies, heavy smokers of many years were 20-30 times more likely than ppl who never smoked to develop lung CA, not just slightly more likely

Question 26

Example of dose-response relationship or biological gradient

Answer 26

The overweight are more likely to develop type 2 DM than those with nl weight. The moderately obese are more likely to become diabetic than the overweight. The very obese are still more likely to become diabetic than the moderately obese. The more the weight, the greater the chance of diabetes.