Spoiler-Effect

A Spoiler is:

A non-winning candidate whose presence on the ballot affects which candidate wins.
The spoiler effect displays the failure of the present Choose-one Plurality voting method in Colorado by terms known as Independence of Irrelevant Alternatives. Approval voting and range voting satisfy the independence of irrelevant alternatives criterion.

Ranked voting methods such as Instant Run-off voting can serve spoilers, but Approval Voting avoids this outcome.

Complete information and examples found here http://www.electology.org/spoiler

Our Approval Voting bill HB17-1281 instructs the Secretary of State to create rules and procedures for Approval Voting elections for use in elections after November 1st of 2017.
Local election supervisors in counties, cities/towns, and special districts need election rules from the Colorado Secretary of State.
Home Rule communities may already use Approval Voting without SoS rules, but find them valuable.
Approval Voting for Colorado seeks additional rules, not a change to existing rules.
Use of Approval Voting will be strictly voluntary by communities and districts that want to try it.