Statistics

Question 1

Define Absolute Risk

Answer 1

The likelihood of an event occurring in a specific group of people

The number of events in a group, divided by the number of people in that group

Question 2

What is the absolute risk control (ARC)?

Answer 2

Absolute risk in the control group (i.e. number of events in control arm divided by total numbers in control arm)

Question 3

What is the absolute risk treatment (ART)?

Answer 3

Absolute risk in the treatment group (i.e. number of events in treatment arm divided by total numbers in treatment arm)

Question 4

Absolute risk reduction

Answer 4

ARC - ART

Question 5

Number needed to treat

Answer 5

1 / Absolute risk reduction

Question 6

Relative Risk

Answer 6

Relative risk is a ratio of the probability of an event occurring in the exposed group versus the probability of the event occurring in the non-exposed group

ART / ARC

Question 7

Relative Risk Reduction

Answer 7

(ARC - ART) / ARC or 1 - RR

Question 8

Sensitivity

Answer 8

TP / (TP + FN)
If someone has a disease,
how often will the test be
positive

Question 9

Specificity

Answer 9

TN / (TN + FP)
If someone doesn’t have a
disease, how often will the
test be negative

Question 10

Positive Predictive Value

Answer 10

TP / (TP + FP)
Probability that if the test result
is positive, the individual does
actually have the disease

Question 11

Negative Predictive Value

Answer 11

TN / (FN + TN)
Probability that if the test result
is negative, the individual
doesn’t actually have the
disease

Question 12

What is Prevalence?

Answer 12

The proportion of a population found to have a condition. e.g. 1 in 10,000.

Question 13

What is Incidence?

Answer 13

The probability of occurrence of a given medical condition in a population within a specified period of time. E.g. 1 in 10,000 per year.

It can be thought of as the rate of proliferation in the population.

Question 14

Odds Ratio

Answer 14

Odds of the event : non-event
OR = 1 is no difference

Question 15

What are the main problems associated with meta-analysis?

Answer 15

Publication bias
Language bias
Replication bias
Requires some homogeneity between studies

Question 16

What is type 1 (α) error

Answer 16

Incorrect rejection of the null hypothesis (that no significant difference exists) - aka finding a difference when none exists

Question 17

What is a type 2 error?

Answer 17

Incorrect acceptance of the null hypothesis - aka finding no difference when one exists

Question 18

What are observational studies?

Answer 18

The investigatordoes not assign exposures, but there can be comparison groups
With comparison groups =>analytical study
- Cohort study
- Case-control study
- Cross-sectional study

Without comparison groups =>descriptive study
- Case report
- Case series

Question 19

What is the hierarchy of medical evidence?

Answer 19

1a) Systematic review of RCTs
1b) Individual well designed RCT
1c) All or none study
2a) Systematic review of Cohort studies
2b) Individual cohort study
3a) Systematic review of case-control studies
3b) Individual case-control study
4) Case-series
5) Expert opinion, bench research, first principles

Question 20

What is the grading of recommendation for scientific literature?

Answer 20

A - Consistent level 1 studies
B - Consistent level 2 or 3 studies, or extrapolations from level 1
C - Level 4 studies, or extrapolations from level 2 or 3
D - Level 5 evidence, or troubling/inconsistent studies at any level

Question 21

Describe the process required for drug approval

Answer 21

Pre-clinical studies
Phase 0
- First in human
- Micro dosing
- Preliminary data on pharmacokinetics

Phase 1
- Healthy volunteers
- Dose-ranging

Phase 2
- Larger groups
- Efficacy testing

Phase 3 => at least 2 required to market
- RCTs to assess efficacy

Phase 4
- Post-marketing surveillance

Question 22

What was the OPTIMISE (2014) trial investigating?

Answer 22

In high-risk patients undergoing gastrointestinal surgery, does a cardiac output-guided haemodynamic therapy algorithm compared to clinician-guided standard therapy reduce death and major morbidity within 30 days?

Question 23

What was the intervention protocol in OPTIMISE?

Answer 23

Colloid and dopexamine administration from induction of anaesthesia to 6 hours after end of surgery guided by LiDCO monitor.
250ml bolus colloid over 5 minutes – positive response if rise in stroke volume of at least 10% sustained for 20 minutes.

Question 24

What was the outcome from OPTIMISE?

Answer 24

There was a reduction in 30 day composite adverse major outcomes, but not statistically significant (p = 0.07).
No difference in other end points

Question 25

What factors affect the positive predictive value?

Answer 25

Sensitivity, specificity and prevalence

Question 26

What is the positive likelihood ratio?

Answer 26

Sensitivity / (1 - specificity)
Effect of a positive test on the probability of disease

Question 27

What is the negative likelihood ratio?

Answer 27

(1 - sensitivity) / specificity
Effect of a negative test on the probability of disease