A new index from the American Enterprise Institute suggests the share of mortgages going to first-time buyers is actually much higher than estimated by National Association of Realtors.

Stephen Oliner and Edward Pinto, co-directors of the AEI’s International Center on Housing Risk, put out their inaugural release of the First-Time Buyer Mortgage Share Index, a new measure of the share of mortgages going to first-time buyers. 

They also announced an index to measure the risk of those loans, the First-Time Buyer Mortgage Risk Index.

The Agency FBMSI averaged 52% over the 12 months ending October 2014. The Combined FBMSI averaged an estimated 46% over the 12 months ending October 2014.

“Discussions about homeownership and credit availability are hampered when not grounded in good measurements of loan availability and risk,” said Pinto. “We developed these new tools to provide accurate information to help inform the conversation.”

The FBMSI is the first time the national first-time buyer share has been calculated using a nearly complete dataset with minimal opportunity for sample error.

AEI is throwing down the gauntlet on NAR, saying that their new index is in contrast to the 2014 survey conducted by the NAR, which was based on responses constituting 0.2% of all purchase loans originated during the 12 month survey period and was voluntary, with responses received from only 9% of those mailed the 127-question survey.

For the July 2013-June 2014 period covered by the NAR’s survey, the center’s combined FBMSI had an average value of 45%, substantially higher than the NAR’s survey finding that first-time homebuyers constituted 36% of purchase loans used to buy a primary residence.

“It is not surprising that the NAR results, which are based on a small and non-random sample, provide an inaccurate picture of the importance of first-time home buyers,” said Oliner. “The FBMSI is as comprehensive as currently possible and will hopefully allow a discussion of the facts on this important issue.”

AEI’s First-Time Buyer Mortgage Risk Index stood at 14.56% in October, up slightly from the average for the prior three months, but up nearly 1 percentage point from a year earlier. The FBMRI is about 3 percentage points higher than the composite National Mortgage Risk Index and about 6 percentage points higher than the repeat homebuyer NMRI.