Lecture 6 (causation, variation, stat sig)

Question 1

Types of asso

Answer 1

• Noncausal asso (flaw –> bias)
• Noncausal asso (confounding)
• Random asso (random variation)
• Causal asso

Question 2

Internal validity

Answer 2

• Assessing design, execution, analysis

- Was it done right or was asso due to bias/confounding/random var?

Question 3

External validity

Answer 3

• Generalizability
• Reqs internal validity
• Externally valid if asso = result of basic human physiology

Question 4

Types of causes (2, not combos)

Answer 4

• Necessary: must precede, w/o which doesn’t develop

- Sufficient: leads to disease, but w/o which disease could develop due to smtg else

Question 5

Types of causes (combos)

Answer 5

• Necessary and sufficient: very rare
• Necessary but not sufficient: all req’d
• Sufficient but not necessary: exposure alone causes, but so do others
• Neither: most chronic diseases

Question 6

Criteria for causality

Answer 6

• Temporal relationship
• Strength of asso
• Dose-response
• Replication of findings
• Biologic plausibility
• Consider alternate explanations
• Cessation of exposure
• Specificity of disease
• Consistency w/other knowledge

Question 7

Inarguable criteria for causality

Answer 7

-Temporal relationship: exposure must precede onset of disease

Question 8

Strength of asso: what does it means for causality

Answer 8

• Stronger asso less likely to be explained by confounding

- But weak assos can be causal, strong assos can be non-causal

Question 9

Overall assessment of asso btwn alc + breast cancer

Answer 9

• Temporality: yes
• Strength: weak (<2)
• Dose-response: yes
• Replication: yes (many not stat sig though)
• Biologic plausibility: some
• Alt explanations considered: yes
• Cessation: no ev
• Specificity: no

Question 10

Point estimate

Answer 10

-Estimate of the asso a study is measuring

Question 11

Test of stat sig

Answer 11

-Prob that an asso occurred due to random variation

Question 12

P value (def and what it means when not sig)

Answer 12

• Prob that asso at least as large as that observed could occur by chance
• When it’s not sig: doesn’t mean it was due to random chance, ev just not strong enough to reject/accept Ho

Question 13

Sig level

Answer 13

-Prob that a sig asso will occur when there really is none

Question 14

Type I error

Answer 14

-Rejectct Ho when it’s really true
-Saying asso exists when it really doesn’t
=alpha

Question 15

Confidence Interval (def and benefits)

Answer 15

• Interval that, w/given prob, contains true value

- Provide more info than p-value

Question 16

Power (def and formula)

Answer 16

-Prob that study will demonstrate an asso if it truly exists

=1-beta

Question 17

Beta

Answer 17

-Prob that a true asso will not be observed

Question 18

Type II error

Answer 18

• Failing to reject false Ho

- Saying asso doesn’t exist when it really does

Question 19

What determines power

Answer 19

• Incidence (cohort): max when 1/2 develop
• Prev of exposure (case-control): max when 1/2 exposed
• Strength of true asso

Question 20

alpha

Answer 20

-Give % of assos expected to be sig due to chance alone (when studying multiple)