[kspaans]

Yup, probably the simplest objective metric to calculate is price-to-income ratio as a measure of "overvalued" in a given location.

[TheTrotters]

Not really. There's no universal law which says that bread has to be X% of local income or that housing has to be Y%.

[kspaans]

You're right, interpreting whether a given price-to-rent ratio is overvalued or not is subjective, but calculating that ratio is (mostly) objective and can make for an apples-to-apples comparison between different locations.