Why?

[Mr. Morden]

All this doesn't explain why turnout in the US is much lower than in nearly all modern democracies. I guess a great part of this is due to the rigidity of the party system and the general deadlock that prevails in all institutions.

What is voter turnout like in the UK and Canada?

[Mr. Morden]

All this doesn't explain why turnout in the US is much lower than in nearly all modern democracies. I guess a great part of this is due to the rigidity of the party system and the general deadlock that prevails in all institutions.

What is voter turnout like in the UK and Canada?

65.1% in UK in 2010, 61.1% in Canada in 2011. And these are countries where turnout is already pretty low compared to places like continental Europe.

According to this, the turnout in the 2008 US presidential election was ~62-63% of eligible voters:

http://en.wikipedia.org/wiki/2008_US_Presidential_Election#Turnout

2004 was a bit less, but not by much.  (Granted the preceding few presidential elections were much lower.)  So not that different from the UK and Canada.  Of course, this assumes that we're talking about turnout as a %age of eligible voters in all cases, rather than VAP, or some other metric.

[Mr. Morden]

Hovering around 45 and 55%?  Has the US ever had a presidential election with turnout as a fraction of eligible voters below 50%?  Wasn't even 1996 above 50%?

In any case, I assume that part of the reason for the US, UK, and Canada being low is because of the electoral system, and the fact that both 1) votes in noncompetitive states or districts are "wasted", and 2) FPTP means that voting for longshot parties is pointless, other than for symbolic reasons.

[Mr. Morden]

What exactly is meant by 'eligible voters?'

Citizens of the country in question who are 18 or older.  Though I take your point that the definition runs into difficulty if you take into account people whose eligibility has been rescinded because of a criminal conviction.

[Mr. Morden]

Hovering around 45 and 55%?  Has the US ever had a presidential election with turnout as a fraction of eligible voters below 50%?  Wasn't even 1996 above 50%?

In any case, I assume that part of the reason for the US, UK, and Canada being low is because of the electoral system, and the fact that both 1) votes in noncompetitive states or districts are "wasted", and 2) FPTP means that voting for longshot parties is pointless, other than for symbolic reasons.

According to this website, it's happened thrice - 1920, 1924, and 1996.

But isn't that measuring turnout as a %age of voting age population?  So, it includes non-citizens in the turnout calculation, which skews the answer downwards.  Is that the same definition of turnout being used when we compare to the turnout of other countries?