I’ve heard this question asked (and answered) quite a lot recently.
Every time, I just think ‘work at what?’

Does a SIB work if it manages to get three parties in a room to sign a contract and agree on a price for one outcome? Therefore, can a SIB be said to have worked before it begins to operate?
Does a SIB work if outcomes are improved for the beneficiaries involved? If money flows from governments to investors?
Does a SIB work if a service provider has correctly under-estimated its ability to change an outcome?
Does a SIB work if the majority of people involved in it report a positive experience?
If governments save money?
If governments get better value for money?
If service providers feel they are better able to pursue their mission?
If we learn?
If we change?
Or perhaps SIBs work if we don’t need them anymore in 5 years!

I’ve listed below 22 reasons that have been given for SIBs as they have been announced around the world. Success could be defined by any of these points.
Better programs and better results for the people who participate in them
1. Improving results for beneficiaries by focussing on outcomes rather than outputs
2. Improve the likelihood of delivering real and sustainable solutions to important social challenges
3. Making effective interventions available to far more people in need than the number that can be reached through traditional state contracts and philanthropy
4. Harnessing the innovation capacity of both investors and service providers for publicly funded services
5. Adding discipline to measuring outcomes for government programs because there is an upfront agreement on how to measure success
6. Improving the evidence base for social services, by mandating measurement and publication of outcomes
7. Accelerating the adoption and implementation of promising programs
8. Accelerating the expansion of evidence-based programs delivered by effective nonprofits
A social finance market
9. Unlocking funds to tackle social issues
10. Growing the social finance and social business sector
11. Providing new financial instruments to harness private investment for the benefit of the community
12. Enabling investors to achieve financial returns and social impact
Government
13. Increasing funding for prevention and early intervention programs in a sustainable manner
14. Improving accountability and transparency for publicly funded services
15. Allowing governments to accept and measure new ideas from external providers, only paying for the ones that deliver
16. Saving Government money
17. Lowering risk for government
18. Savings can be recaptured and reinvested into a permanent funding stream for the program
Service providers
19. Increasing accessibility of payment by results contracts
20. Giving nonprofit providers a committed funding stream not subject to budget cuts
Collaboration
21. Aligning the interests of beneficiaries, nonprofit service providers, private investors, and governments
22. Facilitated coordination with organisations working on overlapping problems

Do SIBs work? What do you mean when you say “Do SIBs work”?