Economic Evaluation of Positron Emission Tomography (PET) in Non Small Cell Lung Cancer (NSCLC), CHERE Working Paper 2007/6

Sensitivity Analysis

There were several assumptions that have had to be made in this model to fill in the
gaps in our knowledge about the resource use and how the staging of NSCLC is conducted,
which are based on weak evidence. Therefore sensitivity analyses are used to evaluate how
changes in assumptions used in economic evaluations change the conclusions of studies.⁴⁶
Therefore to test the robustness of the model and the cost effectiveness of PET several one way
sensitivity analyses, a two way sensitivity analysis and a probabilistic sensitivity analysis were
carried out on a number of parameters.

PET accuracy

The first sensitivity analysis that was undertaken was to look at the accuracy of PET
scanning for staging N2/N3 patients using the confidence intervals from the HTBS meta-
analysis as the upper and lower limits of PET sensitivity and specificity. In the NICE meta-
analysis for the sensitivity and specificity of detecting distant metastasis there were no
confidence intervals given. Therefore, a value of 6% lower and 4% higher than the point
estimate was allocated to the PET sensitivity giving a lower limit of 87.4% and upper limit of
96.7% this is roughly consistent with the confidence intervals around the sensitivity and
specificity of PET found in the HTBS meta-analysis. See table 10 below.

Table 10 Sensitivity analysis of PET sensitivity and specificity for CT Negative and CT
positive patients

The main direct impact of lowering the sensitivity and specificity is that the number of
futile operations and missed operations increases in both CT negative patients and CT positive
patients in the PET strategy. This causes more false negatives in both to be incorrectly sent

⁴⁶ Drummond et al, Methods for the Economic Evaluation of Health Care Programmes; Third edition. (Oxford,
O.U.P, 2005), p. 42.

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