Page 32 - 15Diarrhoeaandvomiting

Scope and methodology

Table 1.2 Levels of evidence for studies of the accuracy of diagnostic tests 26

Level Type of evidence
a
Ia Systematic review (with homogeneity) of level-1 studies b
Ib Level-1 studies b
c
II Level-2 studies ; systematic reviews of level-2 studies
III Level-3 studies ; systematic reviews of level-3 studies
d
IV Consensus, expert committee reports or opinions and/or clinical experience without
explicit critical appraisal; or based on physiology, bench research or ‘first principles’
a Homogeneity means there are no or minor variations in the directions and degrees of results between individual
studies that are included in the systematic review.
b Level-1 studies are studies that use a blind comparison of the test with a validated reference standard (gold standard)
in a sample of patients that reflects the population to whom the test would apply.
c Level-2 studies are studies that have only one of the following:
• narrow population (the sample does not reflect the population to whom the test would apply)
• use a poor reference standard (defined as that where the ‘test’ is included in the ‘reference’, or where the ‘testing’
affects the ‘reference’)
• the comparison between the test and reference standard is not blind
• case–control studies.
d Level-3 studies are studies that have at least two or three of the features listed above.

Evidence was synthesised qualitatively by summarising the content of identified papers in a
narrative manner with brief statements accurately reflecting the evidence and producing evidence
tables. Quantitative synthesis (meta-analysis) was performed where appropriate.

Summary results and data are presented in the guideline text. More detailed results and data are
presented in the evidence tables on the accompanying CD-ROM. Where possible, dichotomous
outcomes are presented as relative risks (RRs) with 95% confidence intervals (CIs), and continuous
outcomes are presented as weighted mean differences (WMDs) with 95% CIs.

1.7.3 Health economics

The aim of the economic input in this guideline was to inform the GDG of potential economic
issues relating to the management of dehydration in children, and to ensure that recommendations
represented a cost-effective use of scarce resources.
It is not possible to perform economic analysis for every clinical question and therefore some
prioritisation is necessary, along the lines suggested in the NICE Technical Manual. Some of
26
the clinical questions do not involve a comparison of alternative courses of action (for example,
What factors are associated with an increased risk of dehydration?) and are not amenable to
economic analysis. For some questions addressing laboratory investigations, the GDG accepted
that these often did not need to be routinely undertaken because such routine investigation
would not be cost-effective, as they rarely affect management or health outcomes.
It was thought by the GDG that economic analysis would be important in formulating
recommendations for the following two clinical questions:
• How do oral rehydration therapy (ORT) and intravenous fluid therapy (IVT) compare in terms
of safety and efficacy, in the treatment of dehydration?
• Which interventions (other than fluid therapy and antibiotic treatment) are effective and safe?
The health economics for the latter question focused on oral ondansetron, an anti-emetic
treatment.
A systematic search for published economic evidence was undertaken for these questions. For
economic evaluations, no standard system of grading the quality of evidence exists and included
papers were assessed using a quality assessment checklist based on good practice in decision-
analytic modelling. Reviews of the limited relevant published economic literature are presented
35
as part of the appendix detailing the original economic analysis.

7