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Sasha van Katwyk et al


Fig. 2. Probability of positive return on investment, probabilistic sensitivity analysis.


Fig. 3. One-way sensitivity analysis, return on investment.


Results


Our base-case analysis shows that TOH invested a cumulative US$624,384 in surgical quality improvement programs targeting SSI incidence from 2010 to 2015. In that same time period, SSI incidence has decreased by 2.88% (average of 0.48% annually) resulting in a cumulative savings from averted SSI cases of US$1,423,460. This represents a return of US$3.07 per dollar invested. The observed positive return on investment is not uniform


across surgical specialties. Figure 1 shows the cumulative ROI per year by surgical specialty in stacked bars, with the single curve representing hospital-wide ROI. Return on investment calcula- tions up to year 2016–2017 are based on a linear average annual SSI incidence rate per specialty, while years following 2016 are extrapolating the predicted returns assuming the same trend into the future. Table 3 displays the surgical specialty-level SSI inci- dence and monthly capacity (ie, number of surgeries). The PSA shows a mean ROI ratio of 2.28 (95% confidence


interval [CI], −0.67 to 7.37). In Figure 2, the y-axis represents probabilities that the quality improvement program offers a positive return on investment, whereas the x-axis shows the


annual percentage reduction in SSI incidence. Using the assumption that SSI incidence has reduced by 0.48% per year over 6 years, the probability that the quality improvement programs to date have netted a positive return on investment is 43%. Including the cost of new admissions (scenario 1) into the


model significantly reduced the expected ROI of the quality improvement program to 0.49 (95% CI, −1.50 to 1.40) due to the lower expected savings per patient. The other 2 scenarios, including (scenario 2) hospital revenue for new patients and (scenario 3) expanding costing perspective to include cost of posthospitalization care for SSI patients, had a significant positive impact on expected ROI, as both assigned higher cost per SSI case and therefore a higher net savings per case averted. Under either scenario, there is a high level of confidence that the return on investments to date net a greater than 2-to-1 return on invest- ment of 3.06 (95% CI, 2.49–3.30) for scenario 2 and 4.12 (95% CI, 2.27–5.02) for scenario 3]. The combination of all 3 scenarios results in a similar probability of being a positive ROI as the primary analysis. The one-way sensitivity analysis (Fig. 3) revealed that the cost


per SSI case introduces the highest level of uncertainty into the model. The second-most influential variable on return on


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