Governments know that by-elections invariably bring a bout of the blues!

I met Noel Treacy at the Fianna Fáil Ard Fheis at the weekend and he was in his usual ebullient form. The former Galway East Deputy shares on characteristic with PC Dixon of Dock Green – he never forgets a face (or a name) and it was instructive to see him work the crowd.

Little did we know that later that night the one political statistic which will be forever associated with Treacy would get a re-airing that night.

In July 1982 Treacy contested the by-election in Galway East for Fianna Fáil following the death of Johnny Callanan. A Fianna Fáil government was in power and there was nothing altogether unusual about a Government TD winning a seat in a stronghold for his own party. Had not Enda Kenny did the same in 1975 when succeeding his late father in a by-election, when a Fine Gael-Labour coalition was in power?

But Treacy's victory came to be marked out – because for almost three decades afterwards, no Government candidate won a by-election.

The duck was broken, ironically, by Patrick Nulty's victory for the Labour Party in the October 2011 when he won the seat left vacant by the death of Brian Lenihan junior.

There might have been particular reasons for that. Most of the Deputies who died in office were in opposition at the time. Brian Lenihan's senior's death in 1996 is a good example: Fianna Fáil was not in Government at the time. When a child or close relation of a deceased politician runs in a by-election the sympathy factor will be, naturally, very high.

That would have had some bearing for example, in Helen McEntee's success in Meath East last year, when she won the contest for the seat left vacant by the death of her father. In doing so, she also broke the pattern.

However, it's not always a given. Galway-born TD Seamus Brennan died in 2008 after a battle with cancer. Inexplicably the government of the day did its usual foostering job and delayed the by-election until the following year. By that stage a narrative of annoyance had built up about the delay.

Even though Brennan's son Shay agreed to run (reluctantly) it did the party little good. A combination of the delay, growing antipathy to the Government and the arrival of a bona fide celebrity candidate worked. George Lee romped up.

The pattern did show up a political reality that different rules apply to by-elections. The rules are not iron-cast (I think the 30 year period when the opposition always won was partly down to chance) but they do apply and parties ignore them at their peril.

The rules are:

Oppositions have a strong chance of taking the seat unless it's immediately after a byelection.

Being the son, daughter or spouse of a deceased politician has the potential to out-trump every other consideration.

The ploy of parachuting in a celebrity may be the most cynical in the rulebook but it works more often than it backfires. George Lee's spectacular success in 2009 is the best example – but his resignation less than a year later shows that voters get wise to it.

The reasons for backing a candidate in a by-election often have little to do with national issues. People are not deciding who is best to run the country. The might want to send a sharp reminder to the government of the day, safe in the knowledge it will continue in power. Or else they go colour-blind in terms of their own party allegiance to vote for a candidate they consider to be particularly deserving.

For more, read this week’s Connacht Tribune.