A war of words broke out yesterday between the companies that compile house price data over claims by RP Data and Rismark that their new suite of residential property price indexes would set the standard for home buyers and investors in the Australian market.In a statement accompanying the launch of the RP Data-Rismark index, the partners said their hedonic index was the first of its kind in Australia and claimed that their indexes were "Australia's most advanced suite of commercially available house prices indexes".Australian Property Monitors managing director Michael McNamara said APM had refined its index in line with research undertaken by the Reserve Bank of Australia over the past couple of years.Residex managing director John Edwards said: "The Residex indexes are well tested and not subject to review. They use a technology that is specially designed by us and, on actuarial review, has been shown to be better than the approach RP Data seems to be trying to develop."The RBA commissioned two house price studies last year. Both found that changes in house prices were difficult to measure because of the change in the composition of the properties in the sample over time. For example, if more low-cost flats than houses are sold in a given survey period, the index will decline even though individual values may not have gone down. The task is made more difficult because the quality of housing changes all the time. It is hard to capture the amount spent on renovation and factor that into a sale price.The three common approaches to measuring house price movements are median price change, repeat sales and hedonics. APM uses an adjusted median measure and Residex uses repeat sales.RP Data-Rismark plans to use all three approaches but prefers hedonics. The Reserve Bank studies concluded that the hedonic and repeat sales methodologies were more advanced but often fell down because the data they required to work well was hard to obtain. It concluded that for practical purposes a "stratified" (adjusted) median price measure would be the best guide.RP Data chief executive Graham Mirabito said his team had been collecting the data necessary to put together a reliable hedonic survey since 2002.APM's McNamara said: "Hedonics works by including a lot of information about the attributes of individual properties. The data is the issue. We have been doing hedonics since 2001 and at this stage we still consider we are working with a small amount of data. You can't create a meaningful index with that amount of data."