EAT FOR HEALTH Australian Dietary Guidelines

EAT FOR HEALTH – AusTRALiAn diETARy guidELinEs
112

The evidence was assessed according to NHMRC levels and grades for recommendations for developers of
guidelines,^42 which allowed each article to be critically appraised and assigned a level of evidence based on a
hierarchy according to the type of research question. As this review looked at causality and intervention research
questions the following hierarchy was used.

Table B3: levels of evidence in the literature review

level I A systematic review of level II studies

level II A randomised controlled trial

level III-1 A pseudorandomised controlled trial

level III-2 A comparative study with concurrent controls:

•   Non-randomised experimental trial

•   Cohort study

•   Case-control study

•   Interrupted time series with a control group

level III-3 A comparative study without concurrent controls:

•   Historical control study

•   Two or more single arm study

•   Interrupted time series without a parallel control group

level IV Case series with either post-test or pre-test/post-test outcomes

Data was extracted from included studies and assessed for strength of evidence, size of effect and relevance of
evidence according to standardised NHMRC processes.32,40-42 The components of the body of evidence; evidence
base (quantity, level and quality of evidence); consistency of the study results; clinical impact; generalisability; and
applicability to the Australian context) – were rated as excellent, good, satisfactory or poor according to standard
NHMRC protocols.38,42 The reviewers then translated the evidence into a draft body of evidence statement. The draft
evidence statements were graded A to D according to standard NHMRC protocols:^42

• Grade A indicates that the body of evidence can be trusted to guide practice

• Grade B indicates that the body of evidence can be trusted to guide practice in most situations

• Grade C indicates that the body of evidence provides some support for the recommendations but care should
be taken in its application

• Grade D indicates that the body of evidence is weak and any recommendation must be applied with caution.

In order to reduce potential risks associated with advice being based on findings of single or only a few studies,
the Working Committee and DAA contractors advised that a minimum of five quality studies were required before
a graded draft evidence statement could be made. The individual studies included in meta-analysis studies were
considered as separate studies.

Once the evidence statements had been drafted and graded, the NHMRC commissioned a methodologist
through the NHMRC methodologist panel, Ms Philippa Middleton from the university of Adelaide, to assist the
Working Committee to ensure that the review activities had been undertaken in a transparent, accurate and
unbiased manner. The methodologist and the Working Committee scrutinised each step of the review process
by accessing the original papers and reviewing the rating of evidence components, and the wording and grading
of each draft evidence statement. As a result, some evidence statements and grades were amended using a
Working Committee consensus approach, and the final evidence statements and grades were agreed.

As nutrition is a continuously evolving area and research studies are published on a regular basis, the Working
Committee also considered results from high quality studies (primarily systematic reviews) published after the
literature review, and where deemed warranted, included the findings and references in the relevant evidence
sections in each chapter. However, only the evidence statements from systematic review of the literature until
2009 were graded.