Statistics

Question 1

how to calculate positive predictive value

Answer 1

TP / (TP + FP)

Question 2

how to calculate negative predictive value

Answer 2

TN / (TN + FN)

Question 3

How to calculate sensitivity

Answer 3

TP / (TP + FN )

Proportion of patients with the condition who have a positive test result

Question 4

How to calculate specificity

Answer 4

TN / (TN + FP)

Proportion of patients without the condition who have a negative test result

Question 5

What is the p value

Answer 5

is the probability of obtaining a result by chance at least as extreme as the one that was actually observed, assuming that the null hypothesis is true

Question 6

What is confounding bias

Answer 6

occurs when there is a causal relationship between an unaccounted factor and the main outcome

Question 7

What type of study are forest plots used in

Answer 7

meta analysis

Question 8

how do forest plots display data

Answer 8

can be used to present and combine data from more than one study

Question 9

what is recall bias

Answer 9

Difference in the accuracy of the recollections retrieved by study participants, possibly due to whether they have disorder or not.

particular problem in case-control studies

Question 10

what is Publication bias

Answer 10

Failure to publish results from valid studies, often as they showed a negative or uninteresting result.

Question 11

what is Expectation bias

Answer 11

in non-blinded trials. Observers may subconsciously measure or report data in a way that favours the expected study outcome.

Question 12

what is the Hawthorne effect

Answer 12

Describes a group changing it’s behaviour due to the knowledge that it is being studied

Question 13

what is Lead-time bias

Answer 13

Occurs when two tests for a disease are compared, the new test diagnoses the disease earlier, but there is no effect on the outcome of the disease

Question 14

clinical trial phases?

Answer 14

phase 0 - exploratory studies
phase 1 - safety assessment
phase 2 - assess efficacy
phase 3- assess effectiveness
phase 4 - Postmarketing surveillance

Question 15

clinical trial phase 0?
exploratory studies

Answer 15

very small number of participants and aim to assess how a drug behaves in the human body. Used to assess pharmacokinetics and pharmacodynamics.

help in determining whether it is feasible to move on to further phases

Question 16

clinical trial phase 1?

Answer 16

safety assessment

Determines side-effects prior to larger studies. Conducted on healthy volunteers

Question 17

clinical trial phase 2
assess efficacy

Answer 17

Involves small number of patients affected by particular disease

May be subdivided into
IIa - assesses optimal dosing
IIb - assesses efficacy

Question 18

clinical trial phase 3?

Answer 18

assess effectiveness

Typically involves 100-1000’s of people, often as part of a randomised controlled trial, comparing new treatment with established treatments

Question 19

clinical trial phase 4?
post marketing surveillance

Answer 19

Monitors for long-term effectiveness and side-effects

Question 20

what is the confidence interval

Answer 20

a range of values within which the true effect of intervention is likely to lie

Question 21

what is the confidence level

Answer 21

likelihood of the true effect lying within the confidence interval is determined by the confidence level.

example a confidence interval at the 95% confidence level means that the confidence interval should contain the true effect of intervention 95% of the time.

Question 22

what can linear regression be used for

Answer 22

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

Question 23

what is regression in terms of correlation

Answer 23

Once correlation between two variables has been shown regression can be used to predict values of other dependent variables from independent variables

Question 24

what is a significance test

Answer 24

A null hypothesis (H0) states that two treatments are equally effective (there is no difference).

A significance test uses the sample data to assess how likely the null hypothesis is to be correct.

Question 25

Significance test types

Answer 25

depends if parametric (can be measured) or non-parametric

Question 26

what is the alternative hypothesis

Answer 26

There is a difference between the two treatments

Question 27

what are parametric studies and examples

Answer 27

significance test which is measurable, usually normally distributed
Student’s t test - paired or unpaired
Pearson’s product moment coefficient - correlation

Question 28

What is the Pearsons test

Answer 28

parametric test, measurable
correlation between numeric variables

Question 29

What is the student t test and difference between paired and unpaired

Answer 29

Parametric test

paired data refers to data obtained from a single group of patients, e.g. Measurement before and after an intervention.

Unpaired data comes from two different groups of patients, e.g. Comparing response to different interventions in two groups

Question 30

What are non parametric test

Answer 30

significance test where cant be measured
Do not require a distribution to meet the required assumptions to be analysed

Question 31

what is the man whitney u test

Answer 31

non parametric significance test
compares ordinal, interval, or ratio scales of unpaired data

Question 32

what is the wilcoxon signed rank test

Answer 32

non parametric signif test

compares two sets of observations on a single sample, e.g. a ‘before’ and ‘after’ test on the same population following an intervention

Question 33

what is the chi-squared test

Answer 33

used to compare proportions or percentages e.g. compares the percentage of patients who improved following two different interventions

Question 34

what is the spearman kendall rank

Answer 34

non parametric test - correlation

Question 35

what is a randomised control trial

Answer 35

Participants randomly allocated to intervention or control group (e.g. standard treatment or placebo)

Practical or ethical problems may limit use

Question 36

what is a cohort study

Answer 36

observational and prospective

Two (or more) are selected according to their exposure to a particular agent (e.g. medicine, toxin) and followed up to see how many develop a disease or other outcome.

The usual outcome measure is the relative risk.

see what happens in future w exposure

Question 37

what is a case-control study

Answer 37

Observational and retrospective.

Patients with a particular condition (cases) are identified and matched with controls.
Data is then collected on past exposure to a possible causal agent for the condition.

The usual outcome measure is the odds ratio.

Question 38

what is a cross-sectional survey

Answer 38

Provide a ‘snapshot’, sometimes called prevalence studies

Provide weak evidence of cause and effect