## Critical Appraisal Glossary

**General glossaries and other useful information:**

Bandolier - Glossary

CEBM - Glossary

Bandolier - Describing results of trials and reviews

CMAJ - Tips for Learners of evidence-based medicine

BMJ Evidence-Based Medicine - Down with odds ratios

CEBM - Likelihood ratios

CEBM - CATMaker (computer-assisted critical appraisal tool) and EBM calculators

Text book - Dictionary of Statistics and Methodology

**Glossary of specific terms**

**Bias**

Bias is systematic error that may “distort the design, execution, analysis and interpretation of research”. There are many types of bias which can occur at any stage of the research design and execution.

Sackett, David L. Bias in analytic research. Journal of Chronic Diseases 1979. 32(1-2):51-63. Doi: 10.1016/0021-9681(79)90012-2

CEBM - Catalogue of Bias

Power calculation

Power calculation

A power calculation is used to calculate the minimum sample size (e.g. of participants) required in order to be reasonably sure of detecting an effect of a given size. It is used to prove that the sample size in a particular study or trial is justified.

See:

Bandolier - statistical power

Effect Size FAQs - How do I calculate statistical power?

*P***-value**

The

*p*-value is the probability that any particular outcome would have arisen by chance. Standard scientific practice usually deems a

*p*-value of less than 1 in 20 (i.e.

*p*<0.05) as statistically significant and a

*p*-value of less than 1 in 100 (

*p*<0.01) as statistically highly significant.

See:

Bandolier -

*p*value

Jerry Dallal's Little Book of Statistical Practice -

*p*value

**Confidence interval**

A confidence interval provides a way of assessing the effects of chance. It aids the interpretation of clinical trial data by showing how small or how large the true size of effect might be.

See:

Bandolier - confidence interval

Useable Stats - confidence interval tutorials

**Experimental event rate (EER)**

The experimental event rate is the rate at which an event (such as a response to a drug or other intervention) occurs in an experimental group, for example, how many times an event occurs in the experimental or intervention group. It is calculated by dividing the number of people in whom the event occurred by the total number of people in the experimental group, then multiplied by 100 to get a percentage.

The calculation of absolute risk reduction, relative risk reduction and number needed are all reliant on the EER.

See also:

Bandolier - experimental event rate

Wikipedia - experimental event rate

**Control event rate (CER)**

The control event rate is the rate at which an event occurs in a control group, for example, how many times an event occurs in the group with no intervention, or using a placebo. It is calculated by dividing the number of people in whom the event occurred by the total number of people in the control group, then multiplied by 100 to get a percentage.

See also:

Bandolier - control event rate

Wikipedia - control event rate

**Absolute risk reduction (ARR)**

Absolute risk reduction is the difference between the event rate in the experimental group and the event rate in the control group. i.e. the difference between the experimental event rate (EER) and the control event rate (CER). It is calculated by subtracting the experimental event rate from the control event rate.

See also:

Bandolier - absolute risk reduction

CMAJ - Tips for Learners of evidence-based medicine

**Relative risk reduction**

This is the percentage reduction in events in the event rate in the treatment group (EER) compared to the event rate in the control group (CER). It is calculated by subtracting the EER from the CER, then dividing by the CER.

See:

Bandolier - relative risk reduction

CMAJ - Tips for Learners of evidence-based medicine

**Number needed to treat (NNT)**

This is the average number of patients that needs to be treated in order for

*one*to benefit from the treatment. So the higher the number needed to treat, the less effective the treatment. It is calculated by dividing 100 by the absolute risk reduction (ARR).

See also:

Bandolier - number needed to treat

CEBM - number needed to treat

Bandolier - ACP article - Using Numerical Results from Systematic Reviews in Clinical Practice

CMAJ - Tips for Learners of evidence-based medicine