Changes to APRA mortgage underwriting standards in May and falling interest rates in recent months have led to quite different outcomes for different lenders.Macquarie Securities found that the amount mortgage lenders are prepared to advance on a given level of income and expenses varies by as much as 27 per cent for owner occupier loans and 48 per cent for investor loans. ANZ has the lowest capacity among the big banks. Macquarie has released the results of its annual mortgage broker survey and mortgage shadow shop, reporting that credit availability tightened by around 5 per cent over the past year, largely as a result of increased focus on expense verification.Investors and families with dependants were most affected by the tightening over the past year.Brokers said that most of the contraction was in the investor segment. Since May, credit availability has started to improve.From the peak of lending activity in 2015, credit availability has fallen by as much as 30 per cent.Macquarie said: "Based on our findings, we believe that housing credit growth trends are likely to remain in the 2 to 3 per cent range over the next 12 months. Additional rate cuts would be incrementally positive for credit availability."We expect the majors to continue to shed market share. As our mortgage broker survey highlighted, the majors have less competitive pricing, more focus on expense verification and take longer to approve applications."Bank of Queensland and Suncorp have "materially longer settlement periods.""The majors need to lower their pricing to reduce the level of refinancing. Our survey highlighted that around 60 per cent of mortgage broker business comes from refinancing loans."Macquarie also conducted a shadow shop. Its mystery shoppers earned A$105,000 a year, paid $1300 a month in rent, had general living expenses of $1200 a month and no personal loans or leases. They had a credit card with an $11,000 limit. They were single, with no dependants and were either a first home buyer or an investor.A shadow shopper presenting as an owner occupier was offered a $561,000 loan by ANZ, $695,000 by Commonwealth Bank, $699,000 by NAB and $669,000 by Westpac. The average of lenders surveyed was $651,000.The average loan-to-income multiple was 6.2 times. ANZ's LTI was the lowest at 5.3 times and NAB's the highest at 6.7 times.For investor shadow shoppers, the average on offer was $790,000. ANZ offered $613,000, Commonwealth Bank $780,000, NAB $840,000 and Westpac $889,000.The average LTI was 7.5 times. ANZ's LTI was the lowest at 6 times and Westpac's the highest at 8.4 times.Macquarie said ANZ's tighter credit standards were only one factor in its loss of market share. Brokers reported that its approval times had increased, service levels had deteriorated and underwriting outcomes were inconsistent.