What's the relationship between competition and rankings?

So,

When you do some keyword research with google adwords some keywords might have a high competition, some of them can be low.
As far as I understand this reflects the bidding people put in for paid results, not organic results.
I keep reading that when trying to choose for keywords, those with low competition are easier to rank for than those
with high competition. But how do they relate? Intuitively I understand that when people are willing to pay a lot of money
to use a certain keyword for CPC then that same keyword might also be desirable for organic search results improved
with SEO. But is there a real quantitative relationship between competition and how easy you can get good rankings
for keywords? Anyone got some numbers, correlations?

Thanks!!

This is like a market law: if there is a rising demand for a product then the price of that product tends to be higher but this is not mandatory.
People buy adwords keywords and/or make SEO many times for the same keywords making the SEO competition correlated with adwords competition.