After the tax credit induced "mini-boom" in the spring, home prices should remained pressured through the end of the year, according to the real estate data provider Altos Research. The average national house price was $474,946 in July, according to the Altos 10-city composite price index. The index fell "significantly" from its high in the summer of last year, when buyers were taking advantage of the homebuyer tax credit. It has declined for the past 11 months. The tax credit expired in April. It's a 0.63% decrease from June but up 0.66% over the last three months. Asking prices for homes fell in 19 of the 26 markets tracked. The biggest declines came in Phoenix at 5.1%, Washington, D.C. at 4.1%, and Miami at 3.3%. While demand is dropping, supply is going up, according to Altos. According to the 10-city composite, there were 311,742 houses in inventory in July, up 2.2% from the previous month and up 3.8% over the last three. Altos measured increases in 22 of the 26 markets. In Washington, D.C., inventories increased 5.6% in July from the previous month, the largest increase in the country. "The market, right now, is a veritable case study of the law of supply and demand," according to the report. "Right now, there's a whole lot of supply, but very, very little demand. The buyers that drove a flurry of activity during the spring have left a deafening silence in their wake." According to the report, even through mortgage rates stay at all-time lows, buyers aren't being swayed, which means these supply and demand trends should continue through the rest of 2010. "Increases in inventory nationwide show that demand simply isn't there. As the market continues to correct itself, and as we head into the seasonally weak fall and winter months, expect more increases in inventory, and likely deepening declines in asking prices," according to the report. Write to Jon Prior.