HaDPop

Question 1

Define incidence rate

Answer 1

Number of new cases, per year, per population IR = new events/(number of people x time)

Question 2

Define incidence rate ratio

Answer 2

Comparing the risk of 2 populations (relative risk)

Question 3

Define prevalence

Answer 3

Measure of the number of people who currently have the disease Prevalence = number of cases/population

Question 4

What does a p value of

Answer 4

The likelihood of value occurring by chance is

Question 5

What is the 95% confidence interval

Answer 5

95% certainty that the true value lies within confidence interval If null hypothesis value inside 95% CI then p>0.05 If null hypothesis value outside 95% CI then p

Question 6

How do you calculate CIs?

Answer 6

Lower bound = IRR/error factor Upper bound = IRR x error factor Error factor = exp (2 x (1/d))

Question 7

Describe a case control study

Answer 7

Start with cases of disease, then get controls for each case (up to 6) Investigate exposure of interest Compare using odds ratio

Question 8

How do you calculate odds ratio?

Answer 8

OR = ad/bc

Question 9

Define incidence

Answer 9

Number of new cases in a given time (absolute risk)

Question 10

What are the strengths of case-control study?

Answer 10

Quick and relatively inexpensive

Possible to look at lots of different exposures in detail

Good for rare outcomes

Question 11

What are the weaknesses of case-control studies?

Answer 11

• Not good for rare exposures
• Prone to information bias and selection bias
• Can be impossible to determine whether disease causes exposure or vice-versa

Question 12

Describe a cohort study

Answer 12

• Compares risk in one group with risk of another group (e.g. Group exposed to asbestos compared to group not exposed to asbestos)
• Follow up disease free individuals over time
• Comparisons made using IRR or SMR (if using reference population)

Question 13

What are the strengths of a conort study?

Answer 13

• Allos for detailed and prospective assessment of exposures, outcomes, confounders
• Good for rare exposures and establishing temporal sequence

Question 14

What are the weaknesses of cohort studies?

Answer 14

• Study and reference populations may not be comparable due to selection bias - e.g. The healthy worker effect
• Often there is limited data on reference population
• Large, time consuming and resource intensive
• Survivor bias
• Not good for rare diseases

Question 15

Describe a radomised control trial

Answer 15

• Clinical trial in which interventions are studied
• Allocate imdividuals into two groups matching sex, age, social class to minimise confounders
• Give one group intervention, give other group placebo or original drug

Question 16

What can cause one treatment to be more successful in a RCT than another?

Answer 16

• Chance - minimised with long run trials
• Patient knows treatment - minimised by blinding
• Treating clinician knows treatment - minimised by blinding
• assessor/investigator knows treatment - minimised by blinding
• One treatment genuinely more effective

Question 17

Describe the placebo effect

Answer 17

• Psychological benefit that derives from, being looked after, cared for more carefully or being on a new ‘special’ treatment

Question 18

What is intension to treat analysis?

Answer 18

• All people in trial are included in analysis, regardless of whether they took treatment or not, or partially completed treatment
• Prwserves true randomisation and elimiating confounding factors

Question 19

Define the Bradford Hill criteria

Answer 19

• S = strength of association
• S = specificity of association
• C = consistency of association
• T = temporal sequene
• D = dose response
• R = reversibility
• B = Biological plausibility
• C = coherence of theory
• A = analogy