Acquire evidence

Question 1

What is internal validity?

Answer 1

Can the evidence given be trusted? i.e are the study results accurate and reliable?

An internally valid study is one which measured what it set out to.

Question 2

What is external validity?

Answer 2

To what extent do the results of a study apply to people outside the study population?

Question 3

What should the risk of bias be like in a study with high internal validity?

Answer 3

Very low

Question 4

What are confounding and bias? What other factor can influence study outcome?

Answer 4

They describe factors that may influence or cause a study’s outcome.

Study outcome may be influenced by chance.

Question 5

What are the types of bias that trialists refer to when assessing risk of bias for RCTs?

Answer 5

The cochrane tool is used which assesses:

Selection bias

Performance bias

Detection bias

Attrition bias

Reporting bias

Question 6

What different terms are used by epidemiologists to describe bias?

Answer 6

Confounding

Selection bias

Information bias

Question 7

Which tool is most reliable when assessing bias?

Answer 7

The cochrane tool

Question 8

What is a confounding factor?

Answer 8

Objective of an experiment: A causes B.

Other causes can cause B that are not A and they are confounding factors..

Question 9

How are confounders minimised or eliminated?

Answer 9

Using several strategies such as randomisation

Question 10

What strategies can be used to reduce confounder effect on observational studies?

Answer 10

Restriction

Matching

Stratification

Statistical Techniques

Question 11

How does randomisation reduce confounder effects?

Answer 11

Random allocation of participants between groups should result in a random and even distribution of confounders between treatment and control groups.

It does not require knowledge of possible confounders making it a good control for both known and unknown confounding factors.

Question 12

What is restriction?

Answer 12

Exclusion or specification which involves screening out participants if they possess a confounder.

Question 13

What are the disadvantages to restriction?

Answer 13

Will slow recruitment

Increases internal validity while decreasing external validity/applicability.

Question 14

What is matching and what are the cons to doing it?

Answer 14

Matching a participant that has a confounder with someone with the same confounder in the control group.

The problem with this is it can be onerous if there are several confounders. The study can no longer examine the effect of a matched variable as a result of this.

Question 15

What is stratification?

Answer 15

After study completion a restriction approach is taken and then comparisons can be made between the 2 groups to confirm the effect of a confounder. This strategy facilitates recruitment and enables assessment of the influence of a confounder.

Question 16

What is bias? What does it do to results?

Answer 16

Systematic error in collecting and interpreting data. Can result in both over and underestimating a study effect.

Question 17

What does bias do to validity of a study?

Answer 17

Bias undermines internal validity of a study.

Question 18

What is selection bias?

Answer 18

Systematic differences between baseline characteristics of the groups that are compared

Question 19

What is performance bias?

Answer 19

Systematic differences between groups in the care that is provided or in exposure to factors other than the interventions of interest. (one group gets looked after or receives more attention than the other)

Question 20

What is detection bias?

Answer 20

Systematic differences between groups in how outcomes are determined.

Differences in how outcomes are measured between groups can be a source of detection bias.

Question 21

What is attrition bias?

Answer 21

Systematic differences between groups in withdrawals from a study

Question 22

What is reporting/publication bias?

Answer 22

Systematic differences between reported and unreported findings.

*Studies with positive outcomes tend to be preferentially published and published faster than negative findings

Question 23

How can attrition bias be avoided?

Answer 23

Over-recruiting

When there is knowledge of the bias, post-hoc analysis strategies can be used.

Question 24

When does attrition bias occur? (what kind of attrition?)

Answer 24

When attrition is NOT random. It must also be at a rate >20%

Question 25

Where is publication bias problematic?

Answer 25

With the production of meta-analyses from the present publications.

Question 26

Why does publication bias happen?

Answer 26

Highly competitive research environment

Career promotion concerns

Competition for funding.

Question 27

What is the funnel plot?

Answer 27

A scatter plot plotting the result (Often standard error of the effect) and precision (odds ratios) of multiple studies.

Question 28

What kind of funnel plot indicates bias?

Answer 28

Asymmetry. The plot should resemble a pyramid.