where PDi is an individual score for document Di, and PPi - the weighting factor for position Pi. Score for
document is as follows: -1 for trash; 0 for non-relevant or duplicate; 1 - related; and 2 - good document.
Document ranking position has weights as follows: 1st - 20; 2nd - 15; 3rd - 13; 4th - 11; 5th - 9; 6th & 7th - 8;
8th & 9th - 6; 10th - 4. Consequently, the final score falls into a range [-50, 100].