An index compiled by the Mortgage Bankers Association suggests lenders have begun to tighten standards for housing finance loans as they prepare to implement new qualified mortgage regulations.

The MBA's Mortgage Credit Availability Index draws on data from the AllRegs Market Clarity product. A decline in the MCAI indicates that lending standards are tightening, while increases in the index are indicative of a loosening of credit, the MBA said.

According to the Association, the Index slid 0.7% to 111.5 in August, the first time it moved down after four consecutive months of increases. The MBA set the MCAI to 100 in March 2012 and reported, by way of comparison, that if had been in existence in 2007 it would have had a value of around 800.

The MBA attributed the drop to less availability of some interest only mortgages as well as lower availability of housing finance loans with terms of more than 30 years. In addition, shifting borrower eligibility requirements on jumbo loans helped lower the MCAI, the association said.

“The slight decline in the MCAI in August reflected a reduction in the availability of certain loan features, particularly interest-only and terms exceeding 30 years,” said Mike Fratantoni, MBA's vice president of research and economics.

“As these loan features are outside of the qualified mortgage (QM) definition, these changes may reflect the beginning of QM implementation, and the fact that Fannie Mae and Freddie Mac are limited to acquiring loans that meet the QM definition,” Fratantoni said.

The MBA said that several factors related to borrower eligibility for housing finance loans go into calculating the MCAI, including credit score, loan type, loan-to-value ratio among others.