Observational Studies

Question 1

What is the equation of point prevalence

Answer 1

The number of people with disease at same time / total population at risk of disease at same time

Question 2

What are 3 types of observational studies

Answer 2

1. Cross sectional study
2. Case control study
3. Cohort study

Question 3

What is a cross sectional study

Answer 3

A study that looks at the prevalence of a disease at one time point only. There is no follow up so exposure and outcome is measured at the same time.

Question 4

What is a case-control study

Answer 4

You take people with the disease and look back at risk factors back in time.

Question 5

What is a cohort study

Answer 5

You take people that are exposed and unexposed then follow in time prospective to identify if they develop the disease.

Question 6

What are the 3 factors to consider in observational study that can change data

Answer 6

Bias
Confounding
Chance

Question 7

What are the 2 main categories of bias

Answer 7

Selection bias

Information bias

Question 8

What are the types of biases within selection bias

Answer 8

Sampling bias
Response bias
Healthy worker effect
Healthy reproducer effect

Question 9

What is sampling bias

Answer 9

Some people may be chosen more than other so this would not represent the general population

Question 10

What is response bias

Answer 10

If the study is using questionnaires some people may not respond so there is a question whether the groups of people that responded compared to people that did not respond are similar

Question 11

What is the healthy worker effect

Answer 11

People that work are likely to be healthy compared to those that do not work as they can have a disability

Question 12

What is the healthy reproducer effect

Answer 12

If Women that have children are selected can be more healthy than women that do not have children as they can be infertile so are unable to have children.

Question 13

What are the types of bias within information bias

Answer 13

Recall bias 
Lost to follow up bias 
Social acceptability bias 
Interviewer bias 
Recording bias

Question 14

What is recall bias

Answer 14

When people with an illness are likely to remember certain things more than healthy people

Question 15

What is a recording bias

Answer 15

When ill people are more likely to have more extensive medical records compared to healthy people

Question 16

What is a interviewer bias

Answer 16

If the interviewer knows the individual has the disease or not

Question 17

What is social acceptability

Answer 17

When the person being interviewed knows what is is socially acceptable so may not be honest about drinking, smoking etc.

Question 18

What is lost to follow up bias

Answer 18

When people that are lost are likely to have the outcome of interest drop out than those that are still within the study.

Question 19

What is confounding

Answer 19

This is when there is a 3rd factor that is giving an association.

Question 20

What is an ecological study

Answer 20

A study where observations are made as a whole group rather than individuals e.g regions such as a county or country etc.

Question 21

How do we adjust for a confounders

Answer 21

With a suitable regression model

Question 22

What are the biases that can occur in a cohort study

Answer 22

Healthy worker effect

Lost to follow up

Question 23

What are the advantages of an cohort study

Answer 23

You can look at rare exposures
You can look at multiple diseases as an outcome
It eliminates recall bias as it can be prospective and not retro prospective

Question 24

What are the disadvantages of cohort studies

Answer 24

Not useful for exploring rare disease as fewer individuals will develop it

Question 25

What are the advantages of case-control studies

Answer 25

You can explore rare diseases

You can explore multiple risk factors

Question 26

What are the disadvantages of case-control study

Answer 26

You can only look at one disease
Recall bias as it is retro prospective
You cant estimate absolute risk because we start with a diseased status

Question 27

What are the biases that can occur in case-control study

Answer 27

Recall bias 
Recording bias 
Interviewer bias 
Response bias 
Sampling bias

Question 28

In a case control study what are we interested in exploring

Answer 28

Odd ratio

Question 29

If we do not find any bias, confounders or chance how do we show that there is a causality

Answer 29

Bradford hill criteria