Cochrane Style Manual
Common abbreviations

In this section: Commonly used abbreviations | Common abbreviations that do not need to be defined | e.g., etc., and i.e. | Currency abbreviations

Commonly used abbreviations

This table lists some abbreviations commonly used in Cochrane reviews. See also Common abbreviations that do not need to be defined and Frequently used names.

absolute risk reductionARR
control group risk (avoid control event rate)CGR
controlled clinical trialCCT
confidence intervalCI
degrees of freedomdf

inverse variance or intravascular

Note: if both terms are abbreviated in a review, use lower case 'iv' for intravascular.

mean difference (avoid weighted mean difference)MD
number needed to treat for an additional beneficial outcome (avoid number needed to treat)NNTB
number needed to treat for an additional harmful outcome (avoid number needed to harm)NNTH
odds ratioOR
Peto odds ratioPeto OR
randomized controlled trialRCT
risk differenceRD
risk ratio (formerly called relative risk in Review Manager 4)RR
standard deviationSD
standard errorSE
standardized mean differenceSMD

Common abbreviations that do not need to be defined

Also note that it is not necessary to define the full unit name of standard SI units (see General guidance on SI units in the section on Units and systems of measurement).

AIDSacquired immune deficiency syndrome
CONSORTConsolidated Standards of Reporting Trials
COVID-19coronavirus disease 2019
DNAdeoxyribonucleic acid
GRADEGrading of Recommendations, Assessment, Development and Evaluation
HIVhuman immunodeficiency virus
MeSH (not MESH or Mesh)Medical Subject Headings
PRISMAPreferred Reporting Items for Systematic Reviews and Meta-Analyses
RNAribonucleic acid
UKUnited Kingdom
USAUnited States of America

e.g., etc., and i.e.

e.g.: an abbreviation for ‘for example’ (from the Latin ‘exempli gratia’) that can be used in lists within the text, when examples are given in brackets, and in tables (for brevity). Use the form ‘e.g.’ with no following comma.

etc.: always write 'etc.' (followed by a full stop) in Cochrane reviews. Use a comma before ‘etc.’ if it follows more than one item in a list. If 'etc.' is used at the end of a sentence, do not use two full-stops.

i.e.: an abbreviation for ‘that is’ (from the Latin ‘id est’) that can be used for lists within the text, when information is given in brackets, and in tables (for brevity). Use the form ‘i.e.’ with no following comma.

e.g. (e.g. men, women, children)e.g.,
i.e. (i.e. men, women, children)i.e.,
etc. (Canada, USA, Germany, etc.)etc

Currency abbreviations

Currencies should be expressed using standard three-letter codes defined by ISO-4217, but as with other abbreviations it is generally helpful to expand on first use.

Common codes include USD (US dollar), EUR (euro), and GBP (pounds sterling)

Full list:

See also: Units and systems of measurement: currencies

Section info
Denise Mitchell (
Describe change
NNTB/NNTH swapped to alphbetical order.
Abbreviations alphabetised
COVID-19 added
RNA added
Text with link to Glossary of terms deleted
Cochrane Review changed to Cochrane review.
Change date
25 April 2024