Research Methodology 3: RCTs and comparing means

Question 1

What is a Randomised controlled trial ?

Answer 1

a study in which participants are allocated randomly between an intervention
(e.g. treatment) and a control group (e.g. no treatment or standard treatment)

Question 2

What is a Confounder?

Answer 2

A confounder is a variable that influences both the dependent variable and independent variable causing a spurious association.

Question 3

What is bias - in terms of statistics?

Answer 3

‘a tendency of an estimate to deviate in one direction

from a true value’

Question 4

What does randomisation ensure?

Answer 4

Confounders will be distributed evenly between the samples

Question 5

What does equipoise provide?

Answer 5

ethical basis for medical research that involves

assigning patients to different treatment arms of a clinical trial.

Question 6

What is clinical equipoise?

Answer 6

genuine uncertainty in the expert medical community over whether one treatment will be more beneficial
than another - not ethical if one is known to be better

Question 7

What is selection bias and when can it occur?

Answer 7

Refers to representativeness of sample to wider population

can happen when participants are asked to volunteer for a study

Systematic differences between baseline characteristics of groups that are compared

Question 8

What is performance bias?

Answer 8

Systematic differences between groups in the care that is provided, or in exposure to factors other than the interventions of interest

Question 9

What is attrition bias?

Answer 9

Systematic differences between groups in withdrawals from a study e.g. one
treatment has more side effects than another

Question 10

What is observer/Detection bias?

Answer 10

• Outcome measure does not adequately capture outcome of interest
• Systematic differences between groups in how outcomes are determined

Question 11

What are 2 ways attrition bias can be overcome?

Answer 11

• Intention to treat analysis – analysed in treatment group they were
randomised to, whatever happens later.

• On-treatment analysis or per-protocol analysis – only analyse
patients who finish the treatment according to the study protocol.

Question 12

What assumptions do parametric tests make?

Answer 12

normally distributed

Question 13

Give 2 examples parametric tests

Answer 13

t-test

ANOVA

Question 14

What are non-parametric tests and give examples?

Answer 14

Described as “Distribution-free tests” as they make fewer assumptions

The order (or "rank") of the values is used rather than the actual
values themselves

Examples: Mann-Whitney tests
Kruskal Wallis
Spearman’s Rho

Question 15

What can the Mann-Whitney U test (Two-sample Wilcoxon ranksum test) be used to compare?

Answer 15

non-normally

distributed continuous variables between groups

Question 16

What can a t-test be used to compare and what are the 5 assumptions made?

Answer 16

continuous variables between groups/quantitative data set comparing the means of two groups if the following assumptions are met:

• Randomly sampled
• Independent observations
• normally distributed
• Variances for each group are equal
• large sample

Question 17

What is categorical data?

Answer 17

(nominal; binary; dichotomous)

e.g. smoking,

Question 18

What is a scale variable?

Answer 18

(continuous; interval)

numeric measurement e.g. height

Question 19

What makes a good RCT?

Answer 19

• Internal validity – is the IV causing the DV in this study?

• External validity – to what extent can these findings be generalised to
other people, situations and times?

Question 20

What is the confidence interval?

Answer 20

• Range within the true value lies
• The confidence interval describes the range of values with a given probability (e.g. 95%) that the true value of a variable is contained within that range.

Question 21

What is the p value?

Answer 21

The p value is the probability that the difference observed could have occurred by chance if the groups compared were really alike.

Question 22

What is blinding?

Answer 22

Depending on the level of blinding participants, staff or the study investigator is unaware of group allocations, Rx and hypothesis

Question 23

What is Type 1 error?

Answer 23

There is no true difference but a difference is observed

False positive

When the null hypothesis is true but you reject it

E.g a man comes in but is told he is pregnant

Question 24

What is a Type 2 error?

Answer 24

True negative predictive value

A true difference exists but is not observed (Type Two True)​

E.g a pregnant women comes in but is told she is not pregnant

Question 25

When would you use chi-squared test?

Answer 25

qualitative data set, categorical outcomes ​

Question 26

When would you use Whitney U test?

Answer 26

quantitative data set where there in no normal distribution.​