Stats

Question 1

What do screening tests rely on

What is it a measure of

Answer 1

Good sensitivity- true positives

Question 2

What measures true negatives

Answer 2

Specificity

Question 3

How do you calculate PPV and NPV

Answer 3

PPV- true +/ (true+ + false +)

NPV- true -/ (true- +false -)

Question 4

What is a type 1 error

What does it give

Answer 4

False positives

P values- normally 0.05%

Question 5

What is a type 2 error

What makes it more likely

Answer 5

False negatives

Of the study is underpowered

Question 6

Which variable won’t change no matter how sick the individuals are

Answer 6

Relative risk

Question 7

How do you calculate relative risk

Answer 7

A/a+b divided by c/c+d

Question 8

How do you calculate odds ratio.

Answer 8

Abxcd

Question 9

How do you calculate absolute risk reduction

What does this allow you to calculate? Why?

Answer 9

Events in control/total control - events in exposure/total exposure

NNT 100/(absolute risk reduction in %)

Question 10

What do the following phases of drug trials focus on 
0-
1-
2-
3-
4-

Answer 10

0- pharmacokinetics and pharmacodynamics
1- safety
2- dosing requirements and some efficacy
3- confirms efficacy- usually against standard of care (RCTs)
4- post marketing

Question 11

What does the Bradford hill criteria assess

What does it not take into account

Answer 11

Evidence for a casual relationship

Sensitivity

Question 12

What are 2 types of experimental studies

Answer 12

Control trials and RCTs

Question 13

What are 2 examples of observational studies

How do they differ

Answer 13

Cohort study- looks prospectively

Case control- looks retrospectively

Question 14

What does an ecological study look for

Answer 14

Variables within a group

Question 15

What is an example of a cross sectional study

Answer 15

Community survey

Question 16

What does selection bias entail? Recall? Confirmation? Confounding?

Which type of study is worst for recall bias

Answer 16

Not randomising
Not following up everyone- worse with case control
Ignoring evidence against your fixed beliefs
Mixing of effects

Question 17

How do you calculate a positive likelihood ratio

“Negative

Answer 17

Sens / (100-spec)

100-sens/specificity

Question 18

Forest plots 
What do they represent 
What does the solid vertical line mean 
What do the boxes mean? What does a big vs small box mean. 
What do the horizontal lines mean
What does the diamond mean

Answer 18

Visual representation of a meta analysis
Line of no effect
Study outcomes. Bigger box means bigger sample size
Confidence intervals of each study
Overall studies. Tips=95% CI

Question 19

What would a highly significant study favouring treatment look like on a forest plot

Answer 19

Diamond far to the right of the line of no effect

Question 20

Forest plot

If the horizontal line crosses the line of no effect what does this mean

Answer 20

The study is not statistically significant!

Question 21

Does sensitivity rule out or in

Answer 21

Rules out!