PPB 1

Question 1

What is a prevalence study?

Answer 1

How many people have a particular disease

Question 2

Strengths of cross sectional studies?

Answer 2

Relatively easy and cheap to conductProvide important information on the distribution and burden of exposures and outcomes. This is extremely valuable for health service planning

Question 3

Weakessess of cross sectional studies?

Answer 3

Only measures prevalent, not incident cases. therefore only limited value for identifying factorsIt can be difficult to establish the time sequence of events

Question 4

What is a case control study?

Answer 4

Starts with groups with and without a disease and looks back to see who has the exposure in the past. Often used to identify risk factors for disease with long latent period

Question 5

Strengths of case control study

Answer 5

Quick and relative cheapGood for studying rare diseaseGood for diseases with long latent periods of time between the exposure and outcome

Question 6

Weakness of case control study

Answer 6

Prone to selection bias, particularly unrepresentative controlsProne to information bias because exposure status is determined after the outcome has occurredCannot establish the sequence of events

Question 7

What are cohort studies?

Answer 7

Without the disease, measure the exposures (risk factors), and then follow-up over time to see who gets the disease (aetiological research)With a particular disease, measure characteristics, then follow up to see who gets particular outcomes (prognostic research)

Question 8

What are strengths of a cohort studies?

Answer 8

Exposure (risk factors) or prognostic factors are measured at the start of the study, before the outcome occurs, so measurement is not biased by the presence or absence of the outcomeCan provide data on the time course of the development of the outcomesMultiple outcomes can be examined

Question 9

What are weaknesses of cohort studies?

Answer 9

Slow and potentially expensiveInefficient for rare diseasesExposure status may change during study (can re-evaluate)differential loss to follow-up may introduce bias

Question 10

What is selection bias?

Answer 10

Error due to systematic differences in characteristics between those who take part in a study and those who do not, so that those recruited are not representative of the reference population, or the comparison groups are not comparable.

Question 11

What is information bias?

Answer 11

This is error arising from systematic differences in the accuracy of information collected between comparison groups