Epidemiology of GMH

Question 1

What two disciplines are GMH made up of?

Answer 1

Social sciences and clinical disciplines.

Question 2

What three outcomes do epidemiological methods give us?

Answer 2

Quantify the burden of disease
What causes the disease
Evaluate interventions to prevent it

Question 3

Who was the father of epidemiology?

Answer 3

Jon Snow, Broadstreet pump and cholera outbreak

Question 4

What are the two theories of cause and effect?

Answer 4

Inductivist:
Francis Bacon 1800
observation leads to the theory
repeated observation develops theory.

Refutionist:
Hume: Uncertainty between cause and effect was impossible to eliminate

Popper:
Scientific knowledge is borne out of uncertainty- So observation is attempt to refute existing theories

In practice we use both induction and deduction

Question 5

What is a hypothesis and how does it guide scientific research?

Answer 5

Often due to induction
It is central to research
Statement that precedes outcome

This ensures research is scientific and driven by theory and observation

Question 6

What are the three elements should a hypothesis have, what function does it serve and what advantages does it give us?

Answer 6

It should be:
Clearly stated,
Refutable
Statement, not question or objective

Serves to shape methodology by providing structure

Adv:
Reduces type 1 errors
Ease of replication
Supports findings

Question 7

What three things can epidemiology do?

Answer 7

Describe: Burden of disease
Explain: Analysis of determinants
Evaluate: Treatments

Question 8

What is a cross-sectional study good for?

Answer 8

To take a snapshot of a moment showing:

Frequency, characteristics and distribution of outcomes

Planning services, raising awareness comparing regions, identifying risk factors

BUT: cannot ascertain direction of cause and effect

Question 9

What does the prevalence bathtub refer to?

Answer 9

In cross-sectional studies, prevalence is the rate of new cases subtracted by the rate of disappearing cases. So in this case reduced numbers of new cases could still increase the prevalence if previous cases have not disappeared.

Question 10

What are the important considerations when constructing a cross-sectional study?

Answer 10

1: Defining your base population:
Person, Place and Time

2: Define and enumerate the sampling frame:
Full pop or some
How to get the data

Question 11

What is selection bias and where can it occur?

Answer 11

Selection bias is the phenomenon of your sample differing from the base population and can occur in every stage of research.

Source population
Sampling Frame
Approached to participate
Willing to participate

Question 12

What is the key aim of a cross-sectional study in GMH?

Answer 12

To determine the burden or prevalence of a disease.

It is calculated by dividing the base population by the number of people with a particular outcome.

BUT you cannot determine cause and effect.

Question 13

Briefly describe the elements of a longitudinal study.

Answer 13

Data collected at two or more time points. Those who already have outcomes are excluded

Aim: To measure the new cases and compare outcomes

Hypothesis,
Identify base population,
Define and measure exposure
Define and measure confounders
Define outcomes
Follow-up and analysis

Question 14

What are confounders?

Answer 14

Other factors that may influence results. (grey Hair and death)

We have to measure it and adjust for it.

Question 15

What are the potential biases that can occur in Longitudinal studies?

Answer 15

Avoid systematic errors: Misclassification of outcome

Observer Bias: Blinding is necessary

Info on cofounders

Loss to follow-up bias: Where participants don’t stick to the end

Question 16

What are random and non-random misclassifications?

Answer 16

Random: Errors in determine exposure made where no link between outcome status

Non-Random: Errors made where there is a link with outcome status

Question 17

What is important in longitudinal studies with regard to the source of data?

Answer 17

It should be the same for base and sample population.

Question 18

Why is a loss to follow up an important consideration?

Answer 18

Due to:

Attrition: Where those exposed are less or more likely to finish

Random or differential attrition: Sample size is reduced

Therefore we should: Maintain contact, and make multiple attempts to contact them

Question 19

What is the basic design for a quasi-experimental study?

Answer 19

Recruitment, baseline measures, intervention and then outcomes and follow-up.

Question 20

How do a Non-randomised control trial and an Uncontrolled before and after study look?

Answer 20

Two groups, one has intervention other does not.

Two groups are compared. Should be as similar as possible.

Uncontrolled:
One group only, before and after test.

Question 21

What is the hierarchy of studies for least to most evidence?

Answer 21

Cross-sectional, Cohort, Quasi-experimental, RCT

Question 22

What 6 considerations should we remember in Quasi-experimental studies?

Answer 22

Useful when we cannot randomise
Must protect against confounding
Hard to get similar groups
Baseline differences should be reported
Cause and Effect not attributable
Good for proof of concept

Question 23

What are the attributes that make RCT the most scientific of all studies?

Answer 23

By randomly assigning the participants the confounders are distributed throughout the control and experimental group.

Question 24

What two ways can RCT still contain bias?

Answer 24

If randomisation is not done correctly.

Randomisation is done correctly, but group differences still exist.

Question 25

In what ways can Randomisation be protected?

Answer 25

Allocation is concealed

Is carried out independently

Measure confounders and distribution in groups.

Use techniques to balance groups (blocking: numbers balanced after each block and stratification: key variables balanced)

Question 26

What is random sampling error and how can we reduce it?

Answer 26

It is the error that occurs due to the difference in the sample not represented in the general pop.

We can reduce this by increasing the sample size

Question 27

What bias still exist in RCT?

Answer 27

Information Bias: Where either the participant or the observer knows who is in each group. Particularly hard in MH.

Loss to follow up: Can be controlled by maximising attempts and imputations.

Question 28

What are the criteria for cause and effect?

Answer 28

Bradford Hill criteria
9 measures:
Strength
Consistency
Specificity
Temporal Sequence
Dose Response
Experimental Evidence
Biological plausibility
Coherence
Analogy

Question 29

What are the two types of Quasi-experimental designs?

Answer 29

Non-randomised control groups and Uncontrolled before and after.