Return on investment in needle and syringe programs in Australia: report

5.7 Sensitivity analysis

Page last updated: 2002

The QALY adjustment factors used in the analysis of effect of NSPs on the quality of life of injecting drug users have been based on estimates from the literature, as described in Section 5.3.1.

In order to test the effect of different QALY factors on the outcomes demonstrated to date, we have conducted sensitivity analysis by increasing the QALY adjustment factor by 5% across all stages of both HIV and HCV. Such an increase could come about with improved methods of treating each disease, which, while perhaps not altering the rate of disease progression or mortality, improve the quality of life in each stage. The effect of this approach is essentially to reduce the QALYs saved by NSPs, as those who might otherwise be infected by HIV or HCV would enjoy a higher quality of life than under our original assumptions.

The alternative QALY values are shown in Table 5.7.1, and the effects of the application of these values shown in Table 5.7.2.

The effect of increasing the quality of life adjustment factor for HIV and HCV is to raise the total number of QALYs for people with these diseases, and hence to reduce the QALY gains made by avoiding them. It should be noted that the effect on HCV, however, is greater than that for HIV. This reflects the fact that the major component of the QALY gains made in HIV is derived from an improvement in the quantity of life saved, whereas HCV QALY gains are made up almost entirely of quality of life effects.

In both instances, the gains made in terms of quality of life effects of NSPs in HIV and HCV remain considerable, and reinforce the importance of this aspect of their effect.

Table 5.7.1 Alternative quality of life values by disease stage of HIV and HCV

Table 5.7.1 is separated into 2 smaller tables in this HTML version for accessibility reasons. It is presented as one table in the PDF version.

HIV

Disease stageQALY Value
Early HIV disease - undiagnosed
0.987
Early HIV disease - diagnosed
0.9135
Progressive HIV disease – undiagnosed
0.945
Progressive HIV disease – diagnosed
0.798
AIDS
0.651
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HCV

Disease stageQALY Value
HCV antibody positive - non-chronic hepatitis C
1.000
Mild chronic hepatitis - undiagnosed
0.987
Mild chronic hepatitis - diagnosed
0.861
Moderate chronic hepatitis – undiagnosed
0.987
Moderate chronic hepatitis – diagnosed
0.861
Compensated cirrhosis – undiagnosed
0.882
Compensated cirrhosis – diagnosed
0.777
Liver failure
0.336
Hepatocellular Carcinoma (HCC)
0.105

Table 5.7.2 Net Present Value, 1991 of QALYs gained for HIV and HCV, alternative QALY values

Discount RateNPV (QALYs)
HIV
NPV (QALYs)
HCV
NPV (QALYs)
HIV & HCV
5%
129,151
22,603
151,754
3%
235,943
35,528
271,471
0%
692,880
87,118
779,998