[gmfawcett]

Yes, though I'd say subjective vs. objective rather than qualitative vs. quantitative. Type safety is a quality, not a quantity (unless you're counting the expressions that type-check!).

[deltaonefour]

Type safety is a quantity measured in type errors.

How many type errors in a language that is not type checked vs. how many errors in a program that is?

The numerical difference is quantitative. You can therefore do data analysis on this. Though a type safe program should in theory have ZERO type errors during runtime.

[gmfawcett]

We can agree to disagree on that. :) By your metric, I can improve type safety simply by weakening the guarantees of my type system.

Putting it another way -- a type safe program, in the limit, should have an infinite number of type errors. :)