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Appendix A

Table A.2 Probabilities used in the analysis

Item Value Range Source
Failure to rehydrate on ORT with paralytic ileus 1.00 N/A GDG
Failure to rehydrate on ORT with no paralytic ileus a 0.039 0.039–0.042 Hartling et al. 83
Failure to rehydrate on IVT 0.029 0–0.029 Hartling et al. 83
Phlebitis with IVT 0.027 0–0.029 Hartling et al. 83
Paralytic ileus with ORT 0.027 0.027–0.04 Hartling et al. 83
a The Cochrane review reported that 0.065 patients fail to rehydrate on ORT. However, this review also reported that
0.027 patients with ORT have a paralytic ileus, which we assume always leads to ORT treatment failure. Therefore,
we have derived the probability of treatment failure in children with no paralytic ileus as follows:
Probability of ORT failure: 0.065
Probability of no paralytic ileus: 1 − 0.027 = 0.973
Probability of ORT failure given paralytic ileus: 1.000
The overall probability of ORT failure is a weighted average of ORT failure in children with and without paralytic
ileus:
Let y = the probability of treatment failure in those without paralytic ileus
(0.973y) + (0.027 × 1.000) = 0.065
y = 0.039
The same method was carried out to derive the upper value of the range.

and IVT as advised by expert opinion within the GDG. Actual costs will vary in different settings
and this can be addressed using sensitivity analysis. A ‘worst case’ sensitivity analysis for ORT
relative to IVT was also undertaken.

The costing method utilised an ‘ingredients’ or bottom-up approach. This involved detailing the
actual resources used in providing treatment (i.e. staffing, consumables, and, where there were
differences between treatments, equipment, capital or facilities), obtaining the unit costs of each
resource item and multiplying by the quantity of resource used to obtain an estimate of total cost.
Unit costs for staff were obtained from Unit Costs of Health and Social Care (2007). 206 This
publication documents unit costs for a range of professional staff working within the health and
social care sector. The costing of staff time includes qualification, training and direct overhead
costs in addition to salary/wages and salary oncosts.
Consumable costs relate to resources that are used up in the provision of treatment. Such resource
items cannot be reused. Medical equipment was costed by annuitising the initial capital outlay
spent on the purchase of equipment over its expected lifespan to give an equivalent annual cost.
The formula for calculating the equivalent annual cost is as follows:

where
E = equivalent annual cost
K = purchase price of equipment
S = resale value
r = discount rate (interest rate)
n = equipment lifespan
*
A(n,r) = annuity factor (n years at interest rate)
This equivalent annual cost can then be divided to obtain an estimate of the daily cost of using
a piece of equipment.

Finally, there are resources associated with using hospital facilities over and above those that directly
relate to rehydration therapy. For example, the ‘hotel costs’ associated with an inpatient admission.

* The annuity factor converts the present value of the equipment into an annuity, which is a series of equal annual payments. This is then
divided by 365 to give an equivalent daily cost.

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