Levels of evidence

The key recommendations and levels of evidence incor­porated in the COPD-X guidelines were originally based largely on the Global Initiative for Chronic Obstructive Lung Disease (GOLD), which used the evidence ranking system of the US National Heart, Lung and Blood Institute (NHLBI) (NHLBI/WHO Workshop Report April 2001). The NHLBI scheme is shown in Box 1. For comparison, the National Health and Medical Research Council (NHMRC) (National Health and Medical Research Council 1998) levels of evidence are also shown, along with the equivalent NHLBI categories.

For this update, the COPD-X Guidelines Committee reclassified NHLBI level A as NHMRC level I and NHLBI level B as NHMRC level II evidence. All citations to NHLBI level C were individually reviewed and reclassified as NHMRC level II, III-2, III-3 or IV evidence. On closer examination, some references originally classified as level C were actually considered level D. As NHLBI level D is not recognised in the NHMRC classification, these levels were removed whilst the bibliographic citations were retained.

Box 1: Levels of evidence
a) National Heart, Lung, and Blood Institute (NHLBI) categories
NHLBI category Sources of evidence Definition

A

Randomised controlled trials (RCTs) extensive body of data

Evidence is from endpoints of well-designed RCTs that provide a consistent pattern of findings in the population for which the recommendation is made. Category A requires substantial numbers of studies involving substantial numbers of participants.
B Randomised controlled trials (RCTs) limited body of data Evidence is from endpoints of intervention studies that include only a limited number of patients, post-hoc or subgroup analysis of RCTs, or meta-analysis of RCTs. In general, category B pertains when few randomised trials exist, they are small in size, they were undertaken in a population that differs from the target population of the recommendation, or the results are somewhat inconsistent.
C Non-randomised trials, observational studies Evidence is from outcomes of uncontrolled or non-randomised trials or from observational studies.
D Panel consensus, judgement The panel consensus is based on clinical experience or knowledge that does not meet the above criteria.
b) National Health and Medical Research Council (NHMRC) levels of evidence and corresponding National Heart, Lung, and Blood Institute categories
NHLBI category NHMRC level Basis of evidence

A

I

Evidence obtained from a systematic review of all relevant randomised controlled trials.
B II Evidence obtained from at least one properly designed randomised controlled trial.
C III-1 Evidence obtained from well-designed pseudorandomised controlled trials (alternate allocation or some other method).
C III-2 Evidence obtained from comparative studies (including systematic reviews of such studies) with concurrent controls and allocation not randomised, cohort studies, case-control studies, or interrupted time series with a control group.
C III-3 Evidence obtained from comparative studies with historical control, two or more single-arm studies, or interrupted time series without a parallel group.
C IV Evidence obtained from case series, either post-test or pre-test/post-test.