Liberals and Nationals not travelling as well as NSW election polling reports imply?

ABC Antony Green’s Election Blog 2 March 2015:

As the NSW election approaches, the Baird government's vulnerability to defeat is being hidden by the reporting of opinion polls.

Opinion polls showing Coalition 2-party preferred result of 53% or 54% are being reported as the Baird government on track for re-election when in all likelihood they indicate a much closer contest with the government at risk of losing its majority.

There are three reasons for this.

The first is a likely change in preference behaviour by minor party and independent voters. Like Queensland, NSW uses optional preferential voting, and the recent Queensland election saw a 20% decline in exhausted preferences and a similar size increase in preference flows to Labor. This factor alone was enough to add another 3% to Labor's state wide 2-party preferred vote compared to polls. If the Queensland experience is repeated in NSW, then the published polls are over-stating the Coalition's 2-party preferred vote.

Second, under optional preferential voting, two-party preferred percentages are exaggerated in favour of the party with the higher first preference vote. In over than half of the state's electorates at the 2011 election, the Coalition outpolled Labor on first preferences by more than two-to-one. Because of the way 2-party preferred percentages are calculated under optional preferential voting, the Coalition margins in these seats are exaggerated. Any reversion to a more normal level of Labor first preference vote in these seats will see larger than expected two-party preferred swings.

The north coast National Party seats of Ballina, Lismore and Tweed all sit on margins of more than 21%. All would be Labor held based on the results of the 2013 federal election and will be seats to watch despite being well beyond the uniform swing. The National Party will also face challenges from Independents and anti-CSG campaigners in a string of seats.

In Sydney, traditional marginal seats like Drummoyne and Ryde have wildly inflated Liberal margins compared to past voting patterns. The same comment applies to Penrith where former Liberal MP Jackie Kelly running as an Independent may also complicate the contest.

The third factor is political geography. The tendency in NSW since the introduction of one-vote one-value electoral boundaries is for the Coalition to win fewer seats than Labor for any given level of two-party preferred vote.

In 1984 Labor polled 52.6% of the 2-party preferred vote and won 58 of the 99 seats. In 2007 Labor polled 52.3% and won 52 of 93 seats. In contrast, the Coalition polled 52.7% of the vote in 1991 and won only 49 of 99 seats.

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