Between 1970 and 2003 hose prices rose by an average 3% per assuming they are talking about inflation adjusted prices gives an average increase of around 6% pa
and this historical growth is being use to predict future growth
I agree with you up to there.
BUT
You then state an average 6% growth over the next 5 years would come close to BIS forecast
This maybe true if property had not had a 200% + increase (especially here in Perth) over the last 5 years
This means to stay within historical growth rates property would have to stagnat for the next 15 to bring the growth of the last five back in line with this historical growth rate
Example
a perth property in 2001 cost $100,000 at the end of 2006 at the peak of the boom it was woth $300,000 (at a very conservative bottom end of the growth that really happened)
The same property valued at $100,000 growing at an average of 6%pa would be worth $300,00 in the year 2020.