Besides its a silly comparison: there's been a reduction in the number of by-elections in time (62 between 1959-1964; 30 between 1974O-1979, 24 between 1987-1992; 18 between 1992-1997; 14 between 2005-2010, and 21 between 2010-2015 - but that includes two by-elections where Tory MPs stood down after defecting to UKIP and a few where Sinn Fein MPs stood down to either end double jobbing or to contest Dail seats so I'd to loath to include them: also limiting my sample to parliaments that went at least four and a half years although the shortest lasting of these was the 1974-79 one) as MPs are typically younger, tend to live longer and are also healthier than they once were.
There's also the factor that the main difference between this parliament and the 1992-1997 one is that then the Tories went in to the parliament with a majority of over 20 which generally is workable in most cases and only lost that late in their term after eight by-election losses (four to the Liberals, three to Labour, one to the SNP: they retained no Tory-held by-election seats) and three defections (Alan Howarth to Labour, Emma Nicholson to the Liberals, and George Gardiner technically to the Referendum Party although he never spoke in parliament as a Referendum Party MP) while in this one they need to get a few opposition votes to pass anything, and the deal with the DUP isn't a coalition or anything strong: its supply and confidence and that's no guarantee for ordinary legislation. Even in the 1992-1997 parliament it took until October 1996 for them to officially lose their majority for good (technically lost it a few times before that as they suspended the whip from Tory MPs, but they still mostly voted with the government in this time) and then they got through the next few months with support from the UUP. The DUP aren't likely to pull their support from the Tories until after March 2019 but once they do the government is defeated: and the DUP - especially the parliamentary DUP which is incredibly old and very very odd - are exactly the sort of party that would probably pull their support over something incredibly odd.
As I wrote on AAD, the big issue here could be Farm Subsidies.
