IRV is attempt to make winner-take-all election systems work by using ranked votes - PR in Multi-Member Districts is a more robust solution

PR and ranked voting overlap and differ in ways confusing.

Ranked voting as in STV or IRV allows voters to mark back-up preferences to be used if or when their first preference is not useful.

IRV assures that at least half the votes will be used to elect the winner - at least theoretically. in many cases winner's vote tally is less than half of votes cast. That is after vote transfers. Voters do not have guaranteed even chance of seeing their vote count.

PR can be list PR or STV (PRCV) or MMP

in PR, 80 to 90 percent of votes are used to elect someone, whether that is secured by vote transfers under STV or by party pooling of votes in list PR and in MMP.

The multiple winners in each district and the fact that each winner wins with same or about same number of votes means that a high proportion of votes used to elect winners, each with its own "unanimous constituency".

(as we see in IRV with half of the votes "thrown out," ranked voting by itself does not give high proportion of effective votes, but yes more than what happens in many cases of FPTP.)

Due to PR's high proportion of effective votes, voters have liberty to vote for who they truly want. Not all votes will be used to elect winners under any system, but with PR the chances are good enough that a high proportion can vote for whom they truly want.

PR means that each candidate or party will win a seat with the same number of votes (as much as possible).

Under STV votes are cast for individual candidates but due to equal number of votes each party takes its due share (almost incidentally)

In list PR each party is given its seats based on party votes. MMP has some of this, but it is watered down by use of single-member districts.

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