a. Are not incomes for just a single-wage earner, they include the combined income for a household (of 2.53 people on average)
b. Are referred to in pre-tax figures, not post-tax.
c. Are not just wage income, but include non-wage income like dividends, capital gains, small business income, fed/state/local government transfers, etc.
d. Are using the median, not the average (mean).
[1] says median household income is apparently 4.8k€/month, so around 58k€/year (before tax). Average housing prices seem to be between 250k and 400k (couldn't find a good source). That would be 4.3~6.9 ratio. (edit: Quality of this estimate is probably still low.)
Personally, I believe (affordability of) average housing prices to be a very useless statistic, due to the extreme regional and local variation in housing prices (and incomes). But maybe I am wrong about that and it is a good indicator.
[1] https://de.statista.com/statistik/daten/studie/261850/umfrag...