HSPH core stats overview

Question 1

What is the standard deviation?

Answer 1

Average distance from the mean

Question 2

What is the standard error?

Answer 2

SD of a sample population

Question 3

Calculate SE

Answer 3

SD/square root of sample size

Question 4

Calculate CI

Answer 4

Mean +/- 1.96xSE

Question 5

Calculate relative risk

Answer 5

RR = a/b

a = risk of x in the treatment group 
b = risk of x in the control group

Question 6

RR of treatment that has no effect is?

Answer 6

RR = 1

Question 7

What is absolute risk?

Answer 7

Risk in the placebo group - risk in the treatment group

Question 8

Absolute risk is used to calculate what?

Answer 8

Calculate the risk in a randomised controlled trial

Question 9

Calculate absolute excess risk (AER)

Answer 9

Risk in exposed group - risk in unexposed group

Question 10

Significance of AER is?

Answer 10

?

Question 11

AER is used in what study type?

Answer 11

Cohort trial

Question 12

Calculate the attributable population

Answer 12

Incidence in the population attributable to exposure/incidence in the population

1 (relative risk - 1) / 1+p (relative risk -1)

p = proportion exposed e.g. 20% = 0.2

Question 13

Absolute risk is used in what study type?

Answer 13

Randomised controlled trial

Question 14

Attributable population is used in what study type?

Answer 14

Cohort study

Question 15

Calculate the odds ratio

Answer 15

a/b
a = odds exposure in cases
b = odds exposure in controls

Question 16

When is the OR used?

Answer 16

In case control studies in place of the RR

Have crude and adjusted

Question 17

What are cluster randomised trials?

Answer 17

Randomise pre-existing groups into one of two treatments e.g. schools, GP surgeries, villages

Question 18

How do you determine a great enough sample size?

Answer 18

Should have a statistical power of at least 80% - usually of at least 85%

Question 19

What is a nested case control study?

Answer 19

Identify a cohort and study them throughout the years

Later years - those who e.g. died are the cases and those that did not die are the controls

Can then look back on the original serum samples to compare the cases and controls

Question 20

What is a cross sectional study?

Answer 20

Snapshot study - measure existing disease and current exposure with no follow up and no questions about history