For the century following Confederation the Liberal Party dominated Prince Edward Island politics.

'After two terms a government starts to use up its energy and vitality.'— Ed MacDonald

Since 1966, however, Islanders have been more even-handed in meting out power. The Liberals still have the advantage — 27 years in government to 18 for the Progressive Conservatives — but a graph of election results shows a pattern suggesting more balance than those raw numbers reveal.

Since the Liberal win in 1966 the pattern is remarkably consistent, with each party holding power for an average of three elections before giving up government. The only break in the three wins and you're out pattern is 1978, when the Liberals won a narrow 17 to 15 seat victory.

UPEI historian Ed MacDonald believes the pattern is connected to the way in which relatively small swings in popular vote can lead to large swings in the number of seats won. For example, in 2007 the Progressive Conservative popular vote fell from 54 per cent to 41 per cent, and the party lost 19 of its 23 seats.

"There has to be a process of renewal, and that can often take an election or two elections before the party kind of rebuilds its sense of optimism and does a rebuilding of leadership and also the rank and file," said MacDonald.

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A political party that loses on P.E.I. ends up in a rebuilding period, says Ed MacDonald. (UPEI)

During that rebuilding it is difficult to challenge the government, which on three of four occasions since 1966 has gone on to an even bigger victory in its second term. After that, the charm begins to fade.

"After two terms a government starts to use up its energy and vitality," said MacDonald.

"The government in power is starting to alienate enough people."

And by the fourth election, enough are alienated that there is a change.

For 50 years, despite vast changes in issues facing P.E.I., the people that have led the province, the entire global political environment, this pattern has remained remarkably consistent.

A changing swing

The future cannot necessarily be predicted from the past, and MacDonald sees one historical trend that could change the pattern.

"I think the swing vote is larger now," he said.

"That could be a function of new immigration, it could be a function of less interest in the political arena among young people, and it's certainly a function of the move from the rural to urban areas. We have a lot more people that are urban and they tend to be more likely to change their vote if a government annoys them. That could be a wild card to break the pattern that we've seen."

How this might change, if at all, is difficult to predict. But it is interesting to note the two most recent governments have experienced even stronger holds on power than those that preceded them. Both the Liberals and the Progressive Conservatives have ruled over legislatures with just one member in the opposition. These more extreme swings may only deepen the trend.