Myself and a colleague work in housing viability studies, and one of the things we've disagreed on is finding the average sales values of a number of properties. The sales value is found by dividing the price it was sold for by the gross internal floor area.
I think the average is found by finding the average of all the sales values, but he thinks it should be found by dividing the total price for all the properties by the total floor area.
e.g. For this table:
In this case my average would be 4092.25 and his 4101.003.
He thinks his average is closer to the "true average" because it ignores outliers more, but I've experimented with this and haven't seen it to be true.
Is there weight to what he's saying? Are there ways of finding an average (besides finding the median) that don't consider outliers?
I think the average is found by finding the average of all the sales values, but he thinks it should be found by dividing the total price for all the properties by the total floor area.
e.g. For this table:
| Price (£) | GIFA (m²) | Sales value (£/m²) |
| 280,000 | 67 | 4179 |
| 280,000 | 65.1 | 4301 |
| 290,000 | 72.1 | 4022 |
| 295,000 | 75 | 3867 |
In this case my average would be 4092.25 and his 4101.003.
He thinks his average is closer to the "true average" because it ignores outliers more, but I've experimented with this and haven't seen it to be true.
Is there weight to what he's saying? Are there ways of finding an average (besides finding the median) that don't consider outliers?
