Lecture 14 - Association & Causality

Question 1

3 types of associations btw exposure and outcome

Answer 1

1. Artifactual
2. Non-causal
3. Causal

Question 2

How do artifactual associations arise?

Answer 2

Can arise from significant bias and/or extensive confounding

Question 3

Koch’s 4 postulates for implicating a causal relationship

Answer 3

1. Must be present in every case of disease
2. Must not be found in cases of other diseases or healthy individuals
3. Must be capable of isolation, culture, and reproducing disease in experimental animals.
4. Must be recovered from experimentally-induced diseased animals

Question 4

Koch’s postulate limitations

Answer 4

• Disease production may require cofactors that postulates don’t address
• Viruses can’t be cultured similar to bacteria
• Not all viruses/bacteria induce clinical disease (carriers & sub clinical disease - unable to be detected)

Question 5

Mill’s Canons

Answer 5

The cause of any effect must consist of a constellation of components that act in concert

Question 6

Synergism

Answer 6

Interaction of 2 or more presumably-causal variables so that the combined effect is clearly greater that the sum of the individual effects.

Question 7

2 ways non-causal associations can occur

Answer 7

1. The disease may cause the exposure

2. Disease and exposure both associated with a third factor (confounding)

Question 8

Examples of 2 ways non-causal associations occur

Answer 8

1. Physical inactivity thought to lead to Arthritis. But actually Arthritis is what causes people to be physically inactive.
2. 3rd or 4th born said to be more likely to have down syndrome. However, not becasue of birth order. It is because mothers are older when 3rd or 4th born and older increases risk of down’s syndrome.

Question 9

Sufficient Cause

Answer 9

Relationship sufficient enough that when cause is present you will always get disease. RARE

Question 10

(T/F) Sufficient causes always act alone in causing a disease.

Answer 10

False, may have multiple required components that collectively act to induce disease

Question 11

Necessary Cause

Answer 11

Necessary for disease to occur, BUT the cause may also be present without disease occurring.

Question 12

Component cause (Risk Factor)

Answer 12

If present, increases probability of a particular disease. Helps prime people for disease. Some patients must be primed or suceptible to disease before component cause can induce disease.

Question 13

Temporality

Answer 13

The necessity that the cause precede the effect/outcome

Question 14

Proximate cause

Answer 14

Short term interval btw cause and disease occurrence in individual

Question 15

Distant cause

Answer 15

Long term interval btw cause and disease occurrence in individual

Question 16

Induction period

Answer 16

Component cause to disease onset

Question 17

Latent period

Answer 17

Disease onset to diagnosis/clinical presentation

Question 18

Which is easier to see association (Proximate or distant cause)?

Answer 18

Proximate, distant may take a long time for disease to show up so hard to determine relationship btw cause and disease becasue exposed to so much more in that long induction period

Question 19

What do you collectively call it when multiple component causes work in concert to cause disease?

Answer 19

Component causes collectively become sufficient cause

Question 20

3 ways to control/adjust for other variables to examine effect of a single factor

Answer 20

1. Restriction - keeps other factors out
2. Matching - similar characteristics in each group
3. Stratification - categorize by disease severity or exposure level

Question 21

Hill’s guidelines/criteria for causal inference

Answer 21

1. Strength
2. Consistency
3. Temporality
4. Biologic gradient
5. Plausibility

Question 22

The higher the # of Hill’s criteria met….

Answer 22

The more likely association MAY be causal

Question 23

Strength

Answer 23

Greater the association the more convincing it is that association MIGHT be causal

Question 24

Consistency

Answer 24

The repeated observation of association in diff populations under diff circumstances in diff studies. Increases strength of likelihood of potential causal relationship.

Question 25

Menopausal hormone therapy

Answer 25

• Benefits of MHT very consistent
• So did official clinical study
• combo estrogen/progesterone group has more heart attacks than non-combo
• Estrogen alone group not same rate of heart attack.
• Watched for another year and saw estrogen alone group also increased heart attacks

Question 26

Why can consistency show wrong effects in some situations like MHT?

Answer 26

Biases

Question 27

Temporality

Answer 27

necessity that disease precede the effect/outcome

Question 28

Explain temporality in higher cancer rates in former smokers during first yr after quit

Answer 28

Substantial portion often quit because have started to see early signs and symptoms of already existing but not yet diagnosed lung cancer

Question 29

Biologic gradient

Answer 29

Observation of gradient of risk (dose response) associated with degree of exposure. Smoke more per day, more likely to have lung cancer

Question 30

Threshold effewct

Answer 30

No effect until certain level of exposure (Alcohol consumption and death)

Question 31

Plausability

Answer 31

Biological feasability that associated can be understood and explained. Is event/exposure biologically plausible if really true?

Question 32

Issue with plausability

Answer 32

Plausability decision may be based on prior beliefs that can be flawed or incomplete. Example: Didn’t know organism (H.pylori) could cause ulcers.

Question 33

Cause

Answer 33

A precursor event/condition/characteristic that is REQUIRED for the occurrence of a disease.