Decision tree
Figure 1 shows the decision tree. The decision node splits the tree into two arms:
  1. Arm 1: the new intervention of providing intravenous co-amoxiclav.
  2. Arm 2 : the current standard practice of offering no antibiotic prophylaxis after operative vaginal delivery; this is represented by the data for the placebo cohort of the ANODE trial.
The assumptions made in constructing the disease pathway reflected in the tree were necessary to clean the data and are as follows7:
The unit cost of resources are outlined in Table 18-15. An explanation of how results from the trial were used to estimate resource use and calculate final terminal node costs can be found in Appendix S1.
The data provided in the ANODE trial posed two issues with regards to modelling.
  1. The ANODE trial reported outcomes as independent events1.
  2. Not all patients that reported primary outcomes had their secondary outcomes measured. This was 3420 patients and 2593 patients respectively1.
Solution to Problem 1: Constructing the decision tree with the numbers reported in the
ANODE trial would imply that the outcomes were independent events1. However, the
likelihood of a clinical outcome such as wound breakdown occurring is affected by other
outcomes such as whether the patient experienced perineal pain. For this reason, using medical literature and an understanding of the healthcare delivery process associated with postpartum infection, conditional probabilities were calculated.
Solution to Problem 2: The decision tree has mutually exclusive nodes that are combinations of primary and secondary outcomes. The nominal reported numbers of patients experiencing secondary outcomes could not be used to calculate conditional probabilities as they would be an underrepresentation. For this reason, the number of individuals experiencing secondary outcomes was standardised by scaling the number up to represent the number of expected outcomes for a cohort of 3420 participants.