There's no need to quantify everything

ESG stands for Environmental, Social, and Governance, and investors are increasingly considering these non-financial factors when identifying companies' risks and growth opportunities.  

About ESG, the Economist writes:

[M]uch of ESG is deeply flawed. The concept’s popularity has been partly fuelled by real-world concerns, especially climate change. Yet it has had a negligible impact on carbon emissions, especially by the biggest polluters. Its attempt to address social issues such as workplace diversity is hard to measure. As for governance, the esg industry does a lousy job of holding itself to account, let alone the companies it is supposed to be stewarding. It makes outsize claims to investors. It puts unmanageable demands on companies. ESG investing: A broken system needs urgent repairs, Economist, 23 July

I share the Economist's scepticism; I dislike the over-formalising and quantification of things that are best left to people's discretion. When certain ESG concerns, or such matters as affirmative action become over-formalised, then politics steps in, the debate becomes polarised and meaningful discussion becomes impossible. 

However, a Social Policy Bond regime would revolve around the targeting of broad, meaningful outcomes, and just about any measure of such outcomes can be gamed and manipulated. (There are workarounds, though. For example, when targeting for improvement the literacy rate of teenage girls in Bangladesh, participants in random surveys would not be specified in advance. so that they couldn't be given more attention than other girls.) As well, there is Campbell's Law to consider: 'The more any quantitative social indicator is used for social decision-making, the more subject it will be to corruption pressures and the more apt it will be to distort and corrupt the social processes it is intended to monitor.'  I'd like, therefore, to see a panel of trusted, impartial experts confirm that any recorded improvements are genuine. Because Social Policy Bonds work best at a large scale - national or global, say - the costs of monitoring and verification would be relatively low.