"We sometimes hear the phrases 'the poorest of the poor' or 'the least of these.' Interested in knowing who they are? They are the disabled in the poorest countries, often rejected as outcasts by their families, left on the street to beg. . . . [But] Our estimates showed that an economic investment in a wheelchair realized an internal rate of return of 122 percent, simply based on the increased income the recipient would earn relative to the cost of the wheelchair, a rate of return that vastly exceeds that of the most productive Fortune 500 companies."
Read this (and much more) in this compelling article by Bruce Wydick.