The Indian vote is maybe 45%, the African maybe 35%. The PPP can win by attracting a few cross ethnic votes as it has the power of incumbency. APNU AFC have to work harder to get these cross ethnic votes.
The PPP, because it is the incumbent, attracts a larger % of non Indian votes, maybe 60% of the Amerindian, 20% of the mixed (TK cited a study) and 5% of the black (or 10% of the black/mixed). APNU basically gets only black and some mixed votes. The AFC have yet to prove that they have a permanent support base.
So while neither party can win an election based on tribal calls alone the PPP still has an advantage. It can buy votes. Intimidate voters (poor people who received houselots). It can bribe polling station officials.
So at the end of the day this is a 50:50 election.
What has the PPP at a disadvantage is that this is the first time that they aren't the presumed winner. But then that might make the tribal calls more powerful as they get Indians (who might have previously not planned to vote) out to vote PPP out of fear of a marauding African dictatorship, should APNU AFC win.
There are many unknowns, the biggest being the extent to which Indians in the 25-35 age range (so outside of the control of their parents) buy into what APNU AFC is selling.
The disaffected blacks/mixed, especially males, who don't vote still might not vote. But then maybe they will.......another unknown, based on whether they see Granger as being interested in them. APNU does seem to be attracting more young faces to their rallies than in prior years when they consisted of mainly middle aged black (not mixed) women.