Selection of studies
One reviewer applied the inclusion criteria to identify those studies potentially eligible for
selection and appraisal based on their abstracts; these studies were retrieved as full text.
The selection criteria were then applied fully to the retrieved studies to identify those to
be appraised and included in the review. Full publications subsequently found not to
meet the inclusion criteria were excluded and reasons for exclusion were documented.
The bibliographies of all publications retrieved were manually searched for relevant
references that may have been missed in the database search (pearling).
Data extraction and appraisal of study methodology
Data from all included studies were extracted by one reviewer and checked by a second
reviewer using standardised data extraction tables that were developed a priori. The
studies included in the review were classified according to the National Health and
Medical Research Council (NHMRC) hierarchy of evidence (NHMRC 2000) (Table 1).
Any differences were resolved through discussion.
Table 1. NHMRC hierarchy of evidence
Level of Evidence Study Design
I Evidence obtained from a systematic review of all relevant randomised controlled trials.
II Evidence obtained from at least one properly designed randomised controlled trial.
III-1 Evidence obtained from well-designed pseudo-randomised controlled trials (alternate allocation or
some other method).
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.
III-3 Evidence obtained from comparative studies with historical control, two or more single arm studies,
or interrupted time series without a parallel control group.
IV Evidence obtained from case-series, either post-test or pre-test/post-test.
(NHMRC 2000)
If systematic reviews were eligible for inclusion in the review, the methodology of these