Statistics

Question 1

When do you use a chi-squared test?

Answer 1

qualitative or semi-quanitative data (e.g. percentages of people saying yes vs no)

Question 2

What tests do you use for normally distributed (parametric) data?

Answer 2

2 groups = students t-test

> 2 groups = anova

Question 3

Non-normally distributed (non-parametric) data

Answer 3

2 groups = Mann-Whitney U test

> 2 groups = multiple

Question 4

When do you use a Wilcoxon signed-rank test?

Answer 4

Pre and post intervention, analysing significance of quantitative, non-parametric data?

Question 5

How do you calculate PPV?

Answer 5

TP / TP + FP

Question 6

How do you calculate positive likelihood ratio?

Answer 6

sensitivity / (1 - specificity)

Question 7

How do you calculate the pre-test odds?

Answer 7

pre-test probability (or the prevalence) / (1 - pre-test prob)

if your pre test prob or prevalence is very small (i.e. less than 1%) it will basically be the same as pre-test odds

Question 8

how do you work out probability from odds?

Answer 8

odds = probability / (1-probability)

Question 9

How do you calculate the post-test odds?

Answer 9

Post test odds = pre-test odds x likelihood ratio

Question 10

How do you calculate the post-test probability?

Answer 10

post-test probability = post-test odds / (1 + post test odds)

Question 11

What are all the steps to working out post test probability?

Answer 11

You need

1) pre test prob (prevalence)
2) Pre-test odds
3) likelihood ratio
4) post-test odds
5) post-test probability

Question 12

How do you calculate number needed to treat?

if reduce mortality from 20% to 15%?

Answer 12

NNT = 1 / absolute risk reduction

= 1 / (5/100)
= 100/5
= 20

Question 13

What is type II error?

Answer 13

a wrongful miss
i.e. failing to detect a significant effect when there is one

inherently related to the power of a study which, with a sufficient sample size, can be maximised to reduce the chance of type II error

Question 14

What is the preclinical phase?

Answer 14

testing of drug in non-human subjects, to gather efficacy, toxicity and pharmacokinetic information

Question 15

what is phase 0?

Answer 15

pharmacokinetics; particularly oral bioavailability and half life of the drug

Question 16

What is phase 1?

Answer 16

Testing of drug on health volunteers for safety, involves testing multiple doses

Question 17

What is phase II?

Answer 17

Testing of drug on patients to assess efficacy and side effects

Question 18

What is phase III?

Answer 18

Testing of drug on patents to assess efficacy, effectiveness and safety

Question 19

What is phase IV?

Answer 19

Postmarketing surveillance - watching drug use in public

Question 20

What is an analytic study?

Answer 20

attempted to quanitfy the relationship between two factors

Effect of intervention or exposure on an outcome

Question 21

What is a non-analytic or descriptive study?

Answer 21

does not try to quantify the relationship, but tries to give us a picture of what is happening in a population

e.g. the prevalence, incidence or experience of a group

descriptive studies include case reports, case-series, qualitative studies and surveys (cross-sectional) studies, which measure the frequency of several factors, and hence the size of the problem

Question 22

The main purpose of randomisation is to

Answer 22

Remove bias in the allocation of treatment

Question 23

What is selection bias?

Answer 23

The 2 groups are intrinsically different due to
- systematic flaws in allocation of patients to each group
Dropouts
Chance