Home prices fell in August for the 25th consecutive month and prices in 10 major markets plunged a record 17.7% year over year, according to a key index of real estate values released Tuesday.

The S&P Case-Shiller Home Price 10-city index dropped 1.1% for the month. The 20-city index recorded a record year-over-year decline of 16.6% with a 1% fall in August.

The indexes compare the sale prices of the same homes each year to determine price trends and are considered one of the most accurate home price gauges.

The hardest hit of all 20 cities on a year-over-year basis was Phoenix, where prices plummeted 30.7% during the past 12 months.

Las Vegas prices plunged 30.6% and Miami sank 28.1%.