7.1 Stats in EBM

Question 1

define incidence

Answer 1

new number of cases of a disease in a population in a given time period

Question 2

define prevalence

Answer 2

all cases of a disease in a given population at a given time

Question 3

define risk ratio/ relative risk

Answer 3

ratio of incidence of group A vs B

RR= Ia/Ib

Question 4

define odds ratio

Answer 4

ratio of ‘odds’ of outcome in exposed group vs unexposed

OR = odds of outcome (exposed) / odds of outcome (unexposed)

Question 5

define absolute risk

Answer 5

risk of acquiring a disease over a given Time period

Question 6

define absolute risk difference

Answer 6

control event rate - intervention event rate

e.g heart disease in smokers 25% vs non 10% = 15% difference

Question 7

define p value

Answer 7

probability of effect observed occurring due to chance alone

smaller p value means small probability that effect was due to chance

usually p <0.05, ie we discount a 5% chance effect

Question 8

disadvantages of p values

Answer 8

cant rule out chance
don’t say size of effect
no range of uncertainty

Question 9

what can help capture the ‘uncertainty’ of a study?

Answer 9

confidence interval

Question 10

what makes confidence interval statistically significant for ratios?

Answer 10

doesn’t include 1

e.g. RR=1.3, CI 1.2-1.6

Question 11

what makes confidence interval statistically significant for mean absolute differences?

Answer 11

cant include 0