NEW YORK ( MainStreet) — Despite healthy gains by the economy and real estate numbers moving northward, a tight credit market is still keeping many qualified potential home buyers out of the market.

According to new research from the National Association of Realtors, single home buyers are struggling in the market compared to married couples due to credit concerns. The study shows single home buyers' overall market share of single buyers declined from 32% in 2010 to 25% in both 2012 and 2013. The numbers are from the association's annual Profile of Home Buyers and Sellers for 2013.

"Single home buyers have been suppressed for the past three years by restrictive mortgage lending standards, which favor dual-income households who are more likely to have higher credit scores," said Lawrence Yun, the association's chief economist. "Not seen in this survey is the elevated level of investors in recent years. The housing recovery would have been much weaker without investors, who often purchase with cash."

In the years up through 2010, single home buyers' overall market was stable — usually moving only one or two percentage points, according to Yun.

Out of those that responded to the survey, 66% of buyers were married couples, 16% were single women, 9% single men, 7% unmarried couples and 2% other. However, in 2010, 58% of buyers who responded were married, 20% were single women, 12% single men and 7% unmarried couples.

The study also showed first-time home buyers slipped to a 38% market share in the past year from 39% in the 2012 survey.

Additionally, 14% of all survey respondents were multi-generational households — which can include adult children and parents and grandparents all living in the same home.

The association doesn't have historic comparisons for this finding but added the question to this year's study because of hearsay around the trend.

"It's another manifestation of the difficulty in obtaining a mortgage, in addition to slow growth in good paying jobs," Yun said.

The median age of first-time buyers was 31 — same as in 2012 — and the median income was $67,400. The typical first-time buyer purchased a home costing $170,000, while the typical repeat buyer was 52 years old and earned $96,000 and bought a home costing $240,000. A full 60% of first-time buyers cited a desire to own a home of their own as the primary reason for buying. For repeat buyers, 16% wanted a larger home, 12% had a job-related move, while another 12% said they just wanted to own a home of their own.

Nearly nine out of 10 buyers financed their purchase. The median down payment ranged from 5% for first-time buyers to 14% for repeat buyers. First-time buyers used a variety of resources for the loan down payment, with 78% tapping into savings, 27% receiving a gift from a friend or relative and 7% receiving a loan from a relative or friend. Some 95% of entry-level buyers chose a fixed-rate mortgage and 40% financed with a low-down payment FHA mortgage.