Page 173 - 15Diarrhoeaandvomiting

Diarrhoea and vomiting caused by gastroenteritis in children under 5 years

Staff
The ‘worst case’ analysis used the minimum time that staff could take in order to complete IVT-
related tasks. Again, these times were estimated by the GDG and represent a relatively low-cost
method of delivering IVT (see Table A.4).
Hospital costs
Reference costs report both upper and lower quartile values for costs of hospital stay in addition
to the national average. The lower quartiles for inpatient IV and further IV stay were used in order
to keep the total costs of delivering IVT to the lowest possible value (see Table A.7).

Results

The results for the baseline and ‘worst case’ analysis are presented in Tables A.12 and A.13, respectively.

Table A.12 Baseline analysis – cost of each strategy and threshold QALY gain necessary for
cost-effectiveness

Strategy Cost Incremental cost Incremental QALY gain needed
ORT £71.08
IVT £701.56 £630.48 0.032

Table A.13 ’Worst case’ sensitivity analysis – cost of each strategy and threshold QALY gain
necessary for cost-effectiveness
Strategy Cost Incremental cost Incremental QALY gain needed
ORT £74.17
IVT £426.01 £351.84 0.018

In Tables A.12 and A.13, the two strategies are ranked in terms of cost, least costly first. With
both therapies, the model assumes that all patients are hydrated within a given time frame and,
because of this, effectiveness is assumed to be equivalent for both treatments. The third column
gives the cost differential between the two treatments. Clearly, if the two treatments are equally
effective in all respects, then ORT, as the cheaper option, is considered cost-effective.

Using the costs of the two strategies we can undertake a form of ‘what-if’ or threshold analysis.
If we have accurately captured the opportunity cost of the two strategies, then the values in
the final column of Tables A.12 and A.13 are indicative of the incremental QALY gain needed
in order for the treatment to be considered a cost-effective option in comparison with the next
cheapest option. In the base case analysis, if IVT provided at least 0.032 QALYs more than ORT,
IVT would be considered cost-effective relative to ORT using NICE criteria. Similarly in the ‘worst
case’ analysis, IVT would need to provide a minimum of a 0.018 QALY gain in order for it to be
considered cost-effective.

This incremental QALY calculation is derived by dividing the incremental cost by £20,000. This is
the value NICE adopts as its willingness to pay benchmark for cost-effectiveness and is obtained
from the NICE Guidelines Manual. 210

One-way sensitivity analysis
Sensitivity analysis is used in economic evaluation to assess how sensitive the results of the model
are to the assumptions made about the model parameters, particularly those parameters where
considerable uncertainty exists as to their actual value. One-way sensitivity analysis involves
*
altering the value of a single parameter, holding all the others constant , to determine how sensitive
the cost-effectiveness conclusion is to the assumptions made about that particular parameter.

* For these analyses it is base case values that are kept constant.

148