Statistics

Question 1

What is the standard deviation?

Answer 1

Measure of how much variation there is from the average set of data

Question 2

Define relative risk reduction

Answer 2

Percentage decrease in risk comparing intervention to control
i.e.
Mediterranean diet decreased risk of heart attack from 2% to 1 % - RRR 50%

Question 3

Define absolute risk reduction

Answer 3

Risk in control - Risk in intervention
i.e. Mediterranean diet decreased risk of heart attack from 2% to 1 % - ARR 1%

Question 4

Risk ratio calculation

Answer 4

Risk in treated group / risk in control

Question 5

Define p value

Answer 5

Probability that results occurred by chance

Question 6

Define confidence interval

Answer 6

Range of value that we can be 95% certain the true value lies within

Question 7

What is paired data?

Answer 7

Two or more measurements taken from the same subject/group

Question 8

What test would you used for paired parametric data?

Answer 8

Paired T test

Question 9

What test would you use for paired non-parametric data?

Answer 9

Wilcoxon matched paired-test

Question 10

What test would you use for unpaired parametric data?

Answer 10

Unpaired T test

Question 11

What test would you use for unpaired non-parametric data?

Answer 11

Mann-Whitney U test

Question 12

NNT calculation

Answer 12

1/ARR

Question 13

Define incidence

Answer 13

Number of new cases per population at given time

Question 14

Define prevalence

Answer 14

Total number of cases per population at a given time

Question 15

What is the relationship between the mean and SD in normal distrution?

Answer 15

68.3% lie within 1 SD of the mean
95.4% lie within 2 SD of the mean
99.7% lie within 3 SD of the mean

Question 16

Define sensitivity

Answer 16

Number of true positives detected by test

Question 17

Define specificity

Answer 17

Number of true negatives detected by test

Question 18

Define positive predictive value

Answer 18

Proportion of those who have a positive test who actually have the disease

Question 19

Define negative predictive value

Answer 19

Proportion of those who test negative who do not have the disease

Question 20

Define a type 1 error

Answer 20

Test rejects a true null hypothesis i.e. false positive

Question 21

What is the null hypothesis

Answer 21

There is no different between the intervention and control

Question 22

What is a type II error?

Answer 22

Test fails to reject a false null hypothesis

Question 23

How can you reduce the risk of a type II error?

Answer 23

Increase the power of the test (sample size)

Question 24

Sensitivity calculation

Answer 24

True positive / (True positive + False negative)

Question 25

Specificity calculation

Answer 25

True negative / (True negative + False positive)

Question 26

Which tests are prevalence dependent?

Answer 26

Positive and negative predictive values

Question 27

Which tests are non prevalence dependent?

Answer 27

Likelihood ratios