I am annoyed by this article -
Laura Kuenssberg: Tory by-election disaster shows power of ‘sofa vote’ - BBC News
"Behind the huge headlines of Labour's victories and the Conservatives' by-election thumpings, it's worth paying attention to voters' instinct - not to choose one party or another, but to stay at home.
The two contests this week in Kingswood and Wellingborough have one important thing in common. In both places, the rise in Labour's share of the vote was dwarfed by the fall in support for the Tories.
"
I looked at the last 20 byelections
The median turnout was 40%. There have been some high turnouts and low ones - but the turnout for the last 2 was around the median.
There seems to be an assumption that Labour voters were more likely to turn out than Conservative voters who were more likely to stay at home.
No one knows that unless they talk to the people who didn't vote - and see if they are typical or atypical of the people who did vote.