Lecture 9- Variable Associations, Causation and the role of Change

Question 1

Koch’s Postulates

Answer 1

Demonstrated association between a microorganism and a disease

1. Organism must be observed in every case of disease
2. Must be isolated and grown in pure culture
3. Pure culture must, when inoculated into a susceptible animal, reproduce the disease
4. Organism must be observed in, and recovered from, the experimental animal

Question 2

Richard Doll and Bradford Hill discovered what

Answer 2

Found strong associations between smoking and lung cancer deaths

Question 3

Hills criteria for causation

Answer 3

1. Strength
2. Consistency
3. Specificity
4. Temporality
5. Biological gradient
6. Plausibility
7. Coherence
8. Experiment
9. Analogy

Question 4

Hill’s strength for causation

Answer 4

Strong associations give support to causal relationship between factor and disease

Question 5

Hill’s consistency for causation

Answer 5

An association has been observed repeatedly

Question 6

Hill’s specificity for causation

Answer 6

Association is constrained to a particular disease-exposure relationship, specific cause leads to specific effect

Question 7

Hill’s temporality for causation

Answer 7

The cause/exposure must be observed before the effect

Question 8

Hill’s biological gradient for causation

Answer 8

Also known as dose response; shows a linear trend in the association between exposure and disease

Question 9

Hill’s plausibility for causation

Answer 9

The association must be biologically plausible form the standpoint of contemporary biological knowledge

Question 10

Hill’s coherence for causation

Answer 10

The cause and effect interpretation of our data should not seriously conflict with the generally known facts of the natural history and biology of the disease

Ex: histopathologic effects of smoking on bronchial epithelium

Question 11

Hill’s experiment for causation

Answer 11

Preventative actions alter the frequency of the outcome

Question 12

Hill’s analogy of causation

Answer 12

Should be similarities between known associations and one that is being evaluated for causality

Ex: persons exposed to secondhand smoke should also have increase in lung cancer risk

Question 13

Multi factorial causality

Answer 13

Many types of causal relationships involve diseases with more than one causal factor

Ex: specific exposures, family history, lifestyle characteristics, environmental influences

Question 14

What are the two models of multifactorial causality

Answer 14

Epidemiological triangle and web of causation

Question 15

Epidemiological triangle

Answer 15

Includes 3 major factors- host, agent, environment

Affected by influences such as time, transmission type, and vectors/fomites

Question 16

What are the 4 illustrations of association

Answer 16

Scatter plots, dose response curve, epidemic curve, contingency table

Question 17

Scatter plot diagram

Answer 17

Closer to the points lie with respect to the straight line of best fit the stronger the association between variable X and Y

Question 18

Dose response curve

Answer 18

Type of correlative association between an exposure and an effect

Threshold refers to the lowest dose at which a particular response occurs

Question 19

Epidemic curve

Answer 19

Plotting of distribution of case by time of onset, aids in identifying the cause of disease outbreak

Question 20

2x2 contingency table

Answer 20

True positive, false positive, true negative, false negative

Question 22

What are 3 major challenges to validity of study designs

Answer 22

1. Internal validity vs external validity
2. Error
3. Bias

Question 23

Internal validity

Answer 23

Degree to which a study has used methodological sound procedures

Question 24

External validity

Answer 24

Ones ability to generalize the results of the study

Question 25

Error

Answer 25

Difference between the value obtained and true value for population

Two general categories: sampling error, non-sampling error

Question 26

Sampling error

Answer 26

Variation that occurs because we are studying a sample rather than an entire population. There will always be natural variation between the different sample that are selected

Question 27

What are 4 ways to express sampling error

Answer 27

Confidence intervals, standard error, margin of error, coefficient of variance

Question 28

Non-sampling

Answer 28

Term for errors that are a result of factors other than using a sample, these result in bias

Question 29

What are 4 common types of bias

Answer 29

Recall bias, selection bias, observer bias, confounding

Question 30

Is bias more prevalent in descriptive or analytic studies

Answer 30

More prevalent in analytic studies

Question 31

How to control recall bias

Answer 31

Aware of limitation when selected study method

Question 32

How to control observer bias

Answer 32

Blind or double blind procedures, script, multiple observers

Question 33

How to control selection bias

Answer 33

Randomization

Question 34

How to control confounding bias

Answer 34

Design phase: think through potential confounders, analysis phase: some types of analysis can control for confounders