biostatistics

Question 1

percentage indicating the actual difference in event rate between control and treatment groups

if 8% of people who receive
a placebo vaccine develop the flu vs 2%
of people who receive a flu vaccine

Answer 1

Absolute Risk Reduction
ARR

then
ARR = 8% − 2% = 6% = .06)

Question 2

ARR = _____ - ______

Answer 2

ARR = control rate - treatment rate
ARR = c/c+d - a/a+b

• remember control event rate - experimental event rate

Question 3

risk ratio formula

Answer 3

risk in exposed / risk in unexposed
(a/a+b) / (c/c+d)

*used usually in cohort

Question 4

risk ratio = 1

Answer 4

no risk from exposure

Question 5

risk ratio > 1

Answer 5

exposure increases risk

Question 6

risk ratio < 1

Answer 6

exposure decreases risk

Question 7

why is risk ratio not used for case control studies

Answer 7

because the RR will be affected by the number of cases taken into account. The RR will vary depending on its size.

Question 8

when can RR=OR

Answer 8

rare disease assumption

prevalence less than 10%

Question 9

the number of patients that need to be treated with a medication to avoid an additional negative outcome

Answer 9

number needed to treat

i.e. superstatin and MI case

Question 10

NNT = __ / __

Answer 10

NNT = 1/ARR (Absolute risk reduction)