Epidemiology 3

Question 1

Why is Bradford Hill used?

Answer 1

Enables us to infer causation from both observational and interventional methods

Question 2

What are the criteria in Bradford hill?

Answer 2

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

Question 3

What is the strength criteria?

Answer 3

The stronger association increases the confidence that an exposure causes an outcome

Question 4

What is the consistency criteria?

Answer 4

Consistent findings across setting tended to rule out error or fallacies that might befall one or two studies

Question 5

What is the specificity criteria?

Answer 5

Specificity describes an association between specific causes and specific effects

Question 6

What caveats are in the specificity criteria?

Answer 6

A specific disease arising among specific workers is valuable in supporting the argument for casualty, but conceded a lack of specificity does not necessarily invalidate a casual relationship

Question 7

Is specificity necessary?

Answer 7

Can be informative when present but its absence conveys very little

Question 8

What is the temporality criteria?

Answer 8

It is insufficient for exposure A and outcome B to coexist A but precede B

Question 9

How is temporality used in observational study?

Answer 9

In observational study design take a cross sectional approach that determines the presence of exposure A and outcome B

Question 10

What is the biological gradient criteria?

Answer 10

A dose response effect (in ‘right’ direction) is a compelling argument for casualty (more cigarettes greater risk of lung cancer)

Question 11

Is biological gradient important?

Answer 11

• Quantification often difficult

- When present it is suggestive but tis absence may be of no value

Question 12

What is the biological plausibility criteria?

Answer 12

• Relationship should be biologically plausible where science is ‘understood’
• When deficient understanding assessing whether a relationship is plausible or not may not be possible

Question 13

What is the coherence criteria?

Answer 13

The association ought to be consistent with the existing theory and knowledge

Question 14

What is the difference between coherence and biological plausibility?

Answer 14

• Seeks to ensure that the association is in keeping withe existing science
• About broader picture, goof when existing scientific theory is correct but if most scientist are wrong, this criteria may support he states quo

Question 15

What is the experimentation criteria?

Answer 15

• Evidence from experimentation should be supportive of the proposed link
• Observational studies will nerve conclusively prove causation

Question 16

Why is experimentation sometimes not possible?

Answer 16

Ethics especially in public health issues

Question 17

What is the analogy criteria?

Answer 17

Drawing upon analogous finding may make inference on the relationship

Question 18

When is analogy important?

Answer 18

• Understanding emergent disease and new association

- Rest on existing knowledge

Question 19

What is correlation?

Answer 19

Linear relationship between two variables

Question 20

Does Bradford Hill give a yes or no?

Answer 20

No, need to have own idea

Question 21

What is internal validity?

Answer 21

• if believe that the association truly exists in that group of patients
• Extent to which findings accurately describe the relationship between exposure and outcome in the context of the study

Question 22

What is external validity?

Answer 22

if applicable to other groups of cancer patients e.g. outside of the population

Question 23

What is external validity the same as?

Answer 23

generalisability

Question 24

What is bias?

Answer 24

any trend in the collection, analysis, interpretation, publication or review of data that can lead to conclusions that are systematically different from the truth

Question 25

What does systematic error lead to?

Answer 25

systematic error in the design or conduct of a study can result in bias - which means observed results may be different from the truth - and hurts validity

Question 26

How do you stop random error?

Answer 26

- Always error expected in measurements - over or under estimate height when measuring due to chance have random error - problem to precisions - large enough sample error cancels each other out

Question 27

What happens if systematically overestimate height?

Answer 27

lead to inaccurate results regardless of sample size

Question 28

What are the three types of validity?

Answer 28

1. Selection bias 2. Information bias 3. Confounding

Question 29

Without internal validity can you consider external validity?

Answer 29

Rarely

Question 30

What is selection bias?

Answer 30

Individuals chance to be included in study sample is related to BOTH the exposure and the outcome - leads to bias estimate of the association between the exposure and outcome

Question 31

What is Berkson's bias?

Answer 31

when hospital based case controlled study and controls are selected among the hospital’s patients (selection bias)

Question 32

What is healthy worker effect?

Answer 32

in occupational studies where active workers are more likely to be healthy compared to those that have retired or stopped working

Question 33

What type of study is really susceptible to section bias?

Answer 33

Case controlled study

Question 34

How do you minimise section bias?

Answer 34

1. Controls representative of target population: in terms of exposure to factors in the study 2. Minimise non-response: if more people decline to participate more likely selection bias introduced 3. Compare respondents with non respondents: to see if systematic differences

Question 35

What is information bias?

Answer 35

Misclassification of the exposure or the disease status or both

Question 36

How can people be misclassified?

Answer 36

some heavy smokers classified as light smokers or some lung cancer patients may not receive correct diagnosis

Question 37

Why does misclassification happen?

Answer 37

- study variables are not properly defined | - flaws in data collection

Question 38

What are two types of flaws in data collection?

Answer 38

1. Interviewer bias | 2. Recall bias

Question 39

What is interviewer bias?

Answer 39

1. interviewer will ask lung cancer or no lung cancer if they have been smoking 2. interviewer may be more thorough interviewing people about past smoking who have been diagnosed with lung cancer or not because they expect lung cancer patients to have been smokers 3. lead to misclassification of exposure status and eventually to a bias odds ratio

Question 40

How do you prevent interviewer bias?

Answer 40

1. Interviewer does not know the disease status of the individual 2. Collection process has been carefully standardised so that the interviewer follows a strictly defined protocol when collection data from participants

Question 41

What is recall bias?

Answer 41

the differential inaccurate recall of past exposure between cases and controls - when all participants have trouble remembering their exposure status but has nothing to do with disease no recall bias

Question 42

How can you prevent recall bias?

Answer 42

- using objective ways to assess exposure for example 1. medical records 2. biomarkers

Question 43

What is non-differential misclassification?

Answer 43

- When exposure status is misclassified but equally among cases and controls - Same term applies with errors determining outcome but occur equally among exposed and non-exposed individuals

Question 44

What is the bias like in non-differential misclassification?

Answer 44

Odds ratio obtained bias towards the null

Question 45

What is misclassification differential?

Answer 45

when errors in determining an individuals exposure status occur unevenly among cases and controls or when errors in the diagnosis of the disease which occur unevenly among exposed and non exposed individuals

Question 46

What is the bias like in differential misclassification?

Answer 46

bias towards or away from the null

Question 47

What is response bias?

Answer 47

describes the tendency of participants to respond to questions in a way that is more socially acceptable

Question 48

Is response bias a type of selection bias?

Answer 48

NO

Question 49

What is non-response bias?

Answer 49

process through which people who do not respond are systematically different to the people who do respond

Question 50

Is non-response bias a type of selection bias?

Answer 50

YES

Question 51

What is Hawthorne effect?

Answer 51

1. usually described as the consequence of participants realising they are being observed and therefore acting differently 2. For example, if you knew you were being studied, you might behave in a slightly different way to normal

Question 52

What are types of information bias?

Answer 52

1. Recall bias 2. Response bias 3. Interviewer bias 4. Diagnostic bias

Question 53

What is confounding?

Answer 53

the effect of an extraneous variable that wholly or partially accounts for the apparent effect of the study exposure, or that masks an underlying true association

Question 54

What can confounding lead to?

Answer 54

bias estimates and misleading results

Question 55

What are the four ways to identify confounding?

Answer 55

1. Knowledge of subject matter 2. Three conditions for confounding 3. Stratification 4. Compare crude and adjusted estimate - Only need one

Question 56

What are the three conditions for confounding?

Answer 56

1. Associated with the exposure in the source population 2. Associated with the outcome in the absence of the exposure 3. Not a consequence of the exposure

Question 57

How do you find knowledge of the subject matter?

Answer 57

Could undertake an evidence review and see what other people have proposed or found

Question 58

How can you stratify?

Answer 58

Look at difference of apparent effect within different population strata

Question 59

What is an effect modification?

Answer 59

After controlling for confounding variable may still be third variable the impact of which on the association between exposure and outcome is so important cannot be ignored

Question 60

When does effect modification exist?

Answer 60

when the strength of the association varies over different levels of a third variable

Question 61

How does effect modification impact the study?

Answer 61

take into account with the way that you report results e.g. so present the stratified results with the antibiotic

Question 62

Should you find a way to control effect modification?

Answer 62

No, natural phenomenon so is is not a problem with the study

Question 63

How can you test for effect modification?

Answer 63

1. Breslow-Day test 2. Q test 3. Interaction terms in regression models

Question 64

What is synergism?

Answer 64

effect modifier potentiates the effect of the exposure

Question 65

What is antagonism?

Answer 65

the effect modifier diminishes the effect of the exposure

Question 66

Why is it valuable to know if something is confounding or effect modification?

Answer 66

1. Addressing a confounded relationship by addressing the exposure exclusively is very unlikely to yield a gain. In example (3), stopping a mother from smoking is unlikely to reverse the childhood mental health outcome. 2. Addressing an exposure where effect modification is apparent may be useful: it may be possible to target an intervention into a more homogeneous pool of participants where a greater impact will be yielded

Question 67

What is a crude model?

Answer 67

- univariate analysis of exposure vs outcome | - simply looking at the impact of the exposure on the outcome – with no consideration of anything else

Question 68

Why is an adjusted model used?

Answer 68

How to identify and account for potential confounding