Offering clients plans in either July or September 2010, the credit card company randomly varied three features to a sample of 19,690 clients: 1) monthly interest rate (3.99%, 7.49% or 11.89%), 2) degree of disclosure (either in a footnote on a one-page advertisement for a "special interest rate" or prominently displayed out of a table with the four payment plan options) and 3) length of the prominently featured payment plan (6, 8, 10 and 12 months). For the length of the featured payment plan, although clients could select any of the four plan lengths the featured plan could act as a nudge for the clients if it were viewed as the "default option."
Note that the likelihood of any of these variations (of interest rate, disclosure and payment plans) was equal throughout.
Additionally, we looked at another larger scale field experiment conducted by the same credit card company with another 103,116 clients in July 2010 who were offered a menu of payment plans. The first group had 34,743 clients at 6.39% with the second group of 49,573 clients at 9.59% and control group of 18,800 clients without an offer. The purpose of this additional experiment was to garner more information on information disclosure and probability of default by measuring impact of enrolling in a payment plan on future repayment.