If you are owner-occupying a 2-4 unit property than the apportion of mortgage interest that corresponds to the portion of the building you occupy is not deductible as a business expense {similar situation for property taxes}.In Canada, I would also recommend you entertain a variable rate mortgage over the "traditional" fixed-rate 5-yr term {a mathematical analysis conducted a few years ago, looking at mortgage rates from the end of WWII to the (then) present, showed that over any 25-year period (conventional amortization in Canada), going with a variable rate mortgage came out ahead of using a fixed rate}.  

As I was poking around at the relationships between jobs and potential predictors of job losses, I started looking at a mathematical representation of something less quantitative, that we are all familiar with.

Any mathematical data if for instance I send out 1K letters?

I think that this is a much better mathematical, long-term approach than parking dollars over and above those needed to stably maintain your life and real estate business in low interest savings accounts.

I've heard various definitions but the only one that made sense to me was simple mathematical quartiles based on monthly rent. 

Don't blame others for having more humility and mathematical intelligence.

Here is the dictionary definition of correlation: a relation existing between phenomena or things or between mathematical or statistical variables which tend to vary, be associated, or occur together in a way not expected on the basis of chance alone.

Missing plaster, floors and walls; but full of dead animals, leaks and holes.So help me out in conquering my fear and putting it back into a mathematical equation.

Having a strong mathematics background, I feel pretty comfortable with my deal analyzing skill.

Given my mathematical background I also think that these issues are much easier  than something like differential equations.