Einliegerwohnung - definition question

As already written, here on the market evaluations resulted in an average of -10% when comparing single-family houses with and without a granny flat. BUT as ypg writes, other factors are likely more decisive, and this 10% from the evaluation could ultimately have been caused by confounders, since the houses did in fact differ.

If the house is truly absolutely comparable in the mentioned aspects, I would assume nearly the same value. However, a very individual factor also comes into play when it comes to selling such a house. Because if you happen to find exactly the person who likes your house just as it is, you will achieve more than if all interested parties have more or less large change requests.

As already written, here in the market evaluations showed an average of -10% when comparing single-family houses with and without a granny flat. BUT as ypg writes, other factors are probably more decisive and this 10% from the evaluation could ultimately also have been caused by confounders, since the houses did differ after all.

Minus 10%? Seriously a loss? As mentioned, the neighboring house does not have a granny flat, but a completely separate apartment with its own front door, whereby the apartment is already very large with 90m² and brings in around €600 rent. Both houses are overall very large.