Levels of Evidence and Key Messages

The Asthma Management Handbook 2006 has been developed by a large multidisciplinary group comprising the NAC Guidelines Committee and expert working groups. Its aim is to provide evidence-based guidance on asthma diagnosis and management.

The key recommendations are presented chapter by chapter in a Summary of Practice Points at the beginning of the chapter, along with their NHMRC levels of evidence. The level of evidence highlights the methodology of the studies contributing to the evidence that underpins the guidelines. Where no level I, II, III or IV evidence was available but there was consensus of opinion among the expert group, these clinical practice points have been allocated a tick.

Practical tips based on clinical experience and consensus of expert opinion have been summarised in Practice Tips boxes throughout the text. These have been allocated a tick.

References are cited throughout the text. The complete reference lists, chapter by chapter, are available in the References section at the end of this handbook.

Designation of Levels of Evidence - National Health and Medical Research Council*

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 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 and and post-test

*These levels of evidence ratings have been adapted from US Preventative Services Task Force (1989) Guide to clinical preventative services: an assessment of the effectiveness of 169 interventions (ed M Fisher). Williams and Williams, Baltimore. Appendix A, p 388. Source: NHMRC. A guide to the development, implementation and evaluation of clinical practice guidelines.

Clinical practice points and practice tips

[√] Recommenced best practice based on clinical experience and expert opinion