Stats

Question 1

How many values lie within 1 2 and 3 SD of the mean

Answer 1

68. 3%
69. 4%
70. 7%

Question 2

Two hundred patients with asthma are recruited. Of these 200, 40 report either one or both parents smoking in the house when they were a child. A further 200 controls who do not have asthma are recruited. Of these people 20 report that one or both parents smoked in the house. What is the odds ratio of asthmatics having been exposed to passive smoking as a child?

Answer 2

2.25

Odds of 40:160 = 1:4
Vs odds of 20:180 = 1:9

Odds ratio is (1/4)/(1/9)
=2.25

Odds is ratio of the number of people who incur a particular outcome to the number of people who do not incur the outcome

Question 3

Calculate number needed to treat:

Percentage of patients having further MI within 3 months
Aspirin 4%
Aspirin + new drug 3%

Answer 3

1/(Absolute risk reduction)

so 1/(0.04-0.03) = 100

Question 4

what is the purpose of a funnel plot?

Answer 4

a funnel plot shows publication bias in meta-analyses - symmetrical means bias unlikely

Question 5

What is hazard ratio

Answer 5

Similar to relative risk but used when risk is not constant to time… Ie survival over time

Question 6

What best describes the characteristics of a negatively skewed distribution?

Answer 6

Alphabetical order so
Mean median mode
Than > is positive and< is negative

Question 7

What is linear regression?

Answer 7

linear regression may be used to predict how much one variable changes when a second variable is changed

Correlation is used to test if there is an association in the first place

Question 8

Calculate absolute risk reduction for group of 40 patients, 2 had particular outcome and out of 40 control 1 had outcome

Answer 8

1/20 - 1/40

= 0.025

Question 9

What is the power of a test

Answer 9

= 1 - the probability of making a type 2 error

Which is accepting the null hypothesis when it’s false

Question 10

Which type of study design is retrospective?

Answer 10

Case-controlled study

Question 11

Which is related to prevalence - sensitivity or positive predictive value

Answer 11

PPV

Question 12

Examples of parametric test

Answer 12

Student t test (one group or two groups)
Pearson (to find correlation)
ANOVA (if more than 2 means compared)

Question 13

Skewed distribution negative and positive

Answer 13

alphabetical order: mean - median - mode

‘>’ for positive, ‘

Question 14

What statistical test do you use for Parametric data, comparing two groups

Answer 14

Student t test unpaired

Question 15

Clinical study phases 1

Answer 15

Pharmacokinetics /dynamics

Question 16

Clinical study phase 2

Answer 16

2a assesses dosing

2b assesses efficacy

Question 17

Clinical study phase 3

Answer 17

Assesses effectiveness

Question 18

Clinical study phase 4

Answer 18

Long-term post marketinf surveillance and side effects

Question 19

Calculate Absolute risk reduction

Answer 19

Control event rate - experimental event rate

Remember rate, i.e. number who had outcome/total

Question 20

Calculate NNT

Answer 20

NNT = 1 / absolute risk reduction

= 1 / ( control rate - experimental rate)

Question 21

Which type of statistical measure is it most appropriate to compare survival time with?

Answer 21

Hazard ratio

• similar to relative risk but is used when risk is not constant to time. It is typically used when analysing survival over time

Question 22

What is the standard error of the mean?

Answer 22

= Standard deviation / sq root of number of patients

Question 23

What percentage of adults will have an IgE level higher than 2 standard deviations from the mean?

Answer 23

2 SD = 95.4%

100-95.4 = 4.6%

There are the two extremes, so just for patients higher is 2.3%

Question 24

Type 1 error Vs type 2 error

Answer 24

Type 1 the null hypothesis is rejected when it is true

Type 2 null hypothesis is accepted when it is false

Question 25

What level of evidence does a study offer which is obtained from a meta-analysis of randomised controlled trials?

Answer 25

1a

Question 26

What is equivalent to the pre-test probability?

Answer 26

Prevalence

Question 27

What is variance

Answer 27

Variance = square of standard deviation

Question 28

Odds of rolling a 6 with dice

Answer 28

1/5 or 0.2

Probability is 1/6