Every facet of the Appraisal is listed in the papers:
When there is differnce in the item, a + or a - dollar value is assigned to it.
The amount varies, according to the Appraiser and the local values.
A new swimming pool may be "worth" $30,000, and an old swimming pool may be "worth" -$12,000.
The AGE of the houses is taken into consideration too, in the same manner.
Virtually every detail can be equalized in the way; except for one: LOCATION. That is why an Appraiser will use a nearby house that is not similar, (and adjust the numbers) rather than use a similar house that is miles away.