Unclear how to recreate sales ratio sample data from open data

[rross0]

Cross posted.

I am trying to create a sample of sales from the Cook County Assessors' Open Data portal for sales ratio studies. In the SOP on sales ratio studies, you have:

• Properties with known characteristic changes. Properties known to have undergone physical and/or legal characteristic changes between the time of sale and assessment are excluded.
• Special properties. Some residential properties classified as 'Single-Family' are valued by the 'Special Properties' division of the Valuations Department. These are excluded from the sales ratio study.

It is unclear to me how to identify these properties from the sales data, or what fields in another data set I can join in to ID these sales.

[ccao-jardine]

Good points! The way this is handled currently is that class 288s (properties with the Home Improvement Exemption, which is strong evidence for a property characteristics change) are excluded automatically, by nature of defining residential classes using class codes.

To recreate our sample from Open Data, use the sale_filter colums to apply exclusions. Then exclude ratios in the top or bottom 5% of your sample in the study.

We should make this more straightforward in our SOPs.