Polling results overstate the probable votes for minority candidates. This has been observed since the 1980's when it first surfaced in the California gubenatorial election involving LA mayor Tom Bradley, a black man.

Why? How much? Is it predictable? There do seem to be some measurable trends especially involving race. 5-10% polling errors seem common. The largest errors result when the minority population is less than 15% of the total.

How much of this stems from undecided or no answer responses? How much of it is lies?