I know this is not an exact science but is a good starting point in analyzing a potential deal.I’d be interested in reading some responses to see if I understand it correctly.

Is 90% of UPB more of an art or a science?

Follow demographics.Longterm means growth and growth means immigration and birthrate.Too often investors make decisions based on today's numbers instead of future projections.It is not rocket science the births have already happened you get a 20 year lead up before they become renters you need to find the markets that are landlord-friendly, the population is booming, and doesn't have risky cycles like hurricanes.I am very conservative on my investments and I because of that I have been able to get huge rents and cashflow that would be hard to beat.

By no means do I have it down to a science. 

These days they have it more down to a science.

Now is kind of an art rather than a science to put numbers on those items but do the base U can based on experience.

Mainly, the systems implemented are fascinating (VA, automated offers, etc.)

You are calculating the projected (discounted) cash flow vs the risk of tenant default vs time needed to manage the property (Return on equity).Coming up with your own NOI is an art as much as a science.

@Grayson Graham, there is some really fascinating discussion on this subject in topic 415 from the irs - https://www.irs.gov/taxtopics/tc415.   

Mainly, the systems implemented are fascinating (VA, automated offers, etc.)