From 'India Development Blog'

India Development Blog links to
Group versus Individual Liability:
A Field Experiment in the Philippines. ABSTRACT:
"Group liability is often portrayed as the key innovation that led to the explosion of the microcredit movement, which started with the Grameen Bank in the 1970s and continues on today with hundreds of institutions around the world. Group liability claims to improve repayment rates and lower transaction costs when lending to the poor by providing incentives for peers to screen, monitor and enforce each other’s loans. However, some argue that group liability creates excessive pressure and discourages good clients from borrowing, jeopardizing both growth and sustainability.
Therefore, it remains unclear whether group liability improves the lender’s overall profitability and the poor’s access to financial markets. We worked with a bank in the Philippines to conduct a field experiment to examine these issues. We randomly assigned half of the 169 pre-existing group liability “centers” of approximately twenty women to individual-liability centers (treatment) and kept the other half as-is with group liability (control). We find that converting to individual liability from group liability but keeping other aspects of group lending such as weekly repayment meeting does not affect the repayment rate, but leads to higher outreach by attracting new clients."

There is a caveat: the experiment is on a sample of individuals who joined a group liability programme earlier.
I have been examining a small programme where the lending is done through a pastor in the parishes he worked. So far ( it is over an year old) the repayments are hundred perecent.