It's a good question. First, a few facts. To begin, we'll borrow from Ned Franks again, who shows here
that, on average between 1945 and 2008, 37% of MPs after an election were new. More recently, that number has gone down (in 2008 it was just under 22%) but the trend is by no means straight. For example, after the 1993 election over 72% of MPs were new. In 1980 it was about 23%, in 1949 it was almost 48%.*
We know a bit about why and the reasons behind it. The first is retirement. On average, about 12% of MPs choose not to run again, which accounts for about one-third of the turnover.** Two profs
at Memorial researched voluntary turnover and found a few things. MPs with narrow victories are less likely to run again, as are those who live far from Ottawa. Quebec MPs are also more prone to turn over, perhaps because of the call to provincial politics is stronger there.
Above all, though, their research suggests that those who come to Ottawa wanting to impact public policies tend to be twice as likely to leave as those who primarily want to serve their constituents or view themselves as members of their party.
The second, and bigger reasons is electoral defeat. On average, one-quarter of MPs lose their election.** I've not seen an analysis of this, but anecdotally MPs tell me that their personal profile gets one about 5-8% of their votes - the rest is due to perceptions of the party and the leader.
So if we think turnover is a problem, we can do one of two things. First, is discourage retirement. If the Memorial profs are correct, this'll require either a small country (!) or more power to individual MPs (which has been the direction of much of Parliamentary reform in the last generation
) or some other change in party management. The provision of pensions after 6 years of service probably don't help either if you want to get people to stick around.
A second, and more powerful, route is to reduce electoral turnover. This is where it gets tricky and pretty undesirable, frankly. We could gerrymander ridings, like in the U.S., so they're safer. We could have fewer elections. We could brainwash voters.....
So is it a problem? Maybe, maybe not. It's a good thing to have fresh minds and a comparatively open political system. Furthermore, it's unclear how realistically we can change it even if we wanted to (although better HR management in politics would be a most welcome change). To paraphrase a wiser observer
than myself, I guess the real question is whether our Parliament is too transient to properly do its job.
** Again, depends on the year. See Franks