Help with real estate statistics.

I am a real estate appraiser in California.

I want to conduct a study that will tell me what certain aspects of properties, like bedrooms, square footage, garages, pool, etc.

Our multiple listing service that I will be using allows me to export all the physical characteristics of a home to an excel spreadsheet.

As an example, I want to find out what a pool is worth.

I'm thinking the best way to do this is to find all sales with pools, within a certain category of homes, like 3 bedroom, 2 baths, 1500-2000 sf, 10-30 years old, located in a certain area.

Then run the same search without pools.

Find the difference which would tell me what the value of a pool is.

My question for the forum is, is this the most reliable and efficient way to find the value of a particular aspect of a home?

Does anyone have any experience with this type of research?

Thanks ahead of time.