Thanks to Sunil for painstakingly putting together the data that makes up the latest PB interactive chart.
This shows the breakdown of aggregate votes secured by the parties in Westminster by-elections starting with the first, Oldham East & Saddleworth, in 2011.
Interestingly, in terms of vote losses, the Tories have done worse than the Lib Dems who on this analysis are doing better overall in these elections than the polls. The Tories and Labour, by contrast, have performed worse.
Labour is up far more than the 4.3% shown while CON losses of 10.6% is much bigger figure than the 3-4% shown regularly in the polling.
What distorts this analysis, of course, is that turnout varies so much in these contests with the yellows benefitting from the three seats where they came second and the one they held on to. Also the distribution of by-elections, for whatever reason, has been heavily to Labour. The coalition partners have defended one by-election each while Labour has defended 13.
In terms of the aggregate totals UKIP comes in fourth place which is a tad different from the hype.