© Bala Paranj 2017

Bala Paranj, Test Driven Development in Ruby, 10.1007/978-1-4842-2638-4_9

9. Pair Ranking

Bala Paranj

(1)Atlanta, Georgia, USA

Pair ranking is a voting system developed in 1987 by Nicolaus Tideman. It selects a single winner using votes that express preferences. It can also be used to create a sorted list of winners.

Problem Domain Analysis

Let’s say we need to rank four choices: A, B, C, and D. To pair-rank these choices, we list them in a column, one beneath the other:

Choice AChoice BChoice CChoice D

We then ask: Which is better, A or B? We mark the choice we decide is bettersay, B.

Choice AChoice B |Choice CChoice D

We then ask why B is better and record our reasoning separately. The voting yields only our preference if we don’t ...

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