The notion that just one thing would control voter turnout would not be correct, as there are so many factors. In some of those 1980s results there was tremendous anger, which I spoke of earlier. It's a big motivation to vote if you're angry about the way things are going. In some elections, if the result looks like a full-blown conclusion, you may not be as motivated, or you might not feel as though it's crucial that you get there, because the direction that you support is likely to get across the line.
I think the one thing that would depress voter turnout consistently would be if there was a long tradition of votes not counting for lots of people. If you were a centre-right supporter living in a very strongly centre-left constituency, then there's just no strong motivation to vote other than out of civic duty. For a lot of democracies, regardless of what electoral system, there has been this lowering as time has gone on. In my opinion, PR can be one of the factors that can assist in preventing that decline going even deeper. If all political parties are genuinely on the side of voters, then it doesn't matter who you vote for, because your vote will count. That's a fairly fundamental and decent thing to be able to promote to voters.