I labeled this graph to suggest that it shows what Rich Rosenberg calls the "on-time collection rate": % of amounts due in a month that are actually paid that month. Grameen might be reporting another variant of the collection rate. I believe it is probably not because:
- Grameen's data tables describe the indicator as "Amount repaid as a percentage of amount due."
- Rich favors the on-time rate as "the most useful collection rate for day-to-day portfolio management." His paper was quoted by Pearl and Phillips and most likely influenced the Grameen Bank's choice of public indicators in 2002.
- The alternative "current collection rate"---amounts paid divided by amounts due---can exceed 100% since it includes delinquent payments. It tends to be volatile for the same reason. Grameen's indicator does not behave this way.