proof of the house price bubble, page-34

You need to take into account dual income not just average wage.
Hypothetically if the primary income eaner is on $80,000.00 and the secondary income eaner on $40,000 the joint income is 120,000 then according to your simplistic formula and removing any other variables an average house price of $ 630000 would equate to 5.25 time earning this would only apply to someone borrowing the full ammount.
if the couple had managed to put a deposit together then this ratio would come down even further.