The Polls 2011 – A Cusum Perspective


As part of a review of the voting intention data from You Gov for 2011, I created a CUSUM chart.

What is a CUSUM chart?

  • CUSUM stands for Cumulative Sum. The horizontal axis line at zero is the mean value for data for the whole year
  • Each piece of data, in order, has the mean subtracted. The difference is then added to the accumulated difference of the previous data points
  • This creates the CUSUM line, which always ends in zero

What does it show?

  • It shows the changes and trends in the data that is not visible by just plotting the headline voting intention data
  • Changes are seen as a change in the direction of the CUSUM line
  • If the CUSUM line bounces slightly back and forth across the zero line, it means normal variation is present. In the case of voting intention it mean sample variation is present
  • If the CUSUM line moves strongly in one direction, or has deep peaks and troughs special variation is present. Special variation is defined as something beyond normal sample variation, and will be caused by specific factors

Why perform a CUSUM analysis?

  •  By understanding the special cause variation, a greater understanding is possible of what has affected a party’s voting intention results

Why use You Gov?

  • You Gov was chosen entirely because of the large amount of available data supplied from a common methodology

Analysis of the CUSUM Chart

Point C1

  • This fall in Conservative support occurred after the resignation of Andy Coulson, David Cameron’s Director of Communication, about allegations regarding phone hacking. David Cameron’s judgement was very much in question

Points L1 and C2

  • The run up to the AV referendum in May and local elections was significant. The large rejection of AV benefited the Conservatives, who were clearly against it, in line with 67.9% of those who voted no
  • Conversely, as both events were the first opportunity to punish Nick Clegg and the Liberal Democrats since forming the coalition, the Liberal Democrat VI took a hit
  • Labour was split over AV, and still suffered post referendum decline

Points L2 and C3

  • From the end of May, both Labour and Conservative had picked up from the still falling Liberal Democrats.
  • In early July Ed Miliband was making a strong stand about phone hacking. This was arguably his finest moment in 2011, leaving David Cameron trailing the mood the of the nation. This is clearly seen in the sharp rise of Labour, and the equally sharp fall for the Conservatives.

Points L2 and C4

  • Following the summer riots, David Cameron had taken a tough stance about dealing with the offenders. The rapid processing and harsh sentencing certainly got public approval, and this is shown by the improvement in Conservative fortunes, at the expense of Labour.

Point C5

  • After a drawn-out saga, Liam Fox resigned over his relationship with Adam Werritty. This returned the spectre of corruption among MPs, and neither of the big three parties benefited. Rather they lost support

Point C6


  • Being in opposition limits a party to simply talking tough, whereas a Government can act tough. When David Cameron has acted tough the polls have been good for him
  • Ed’s greatest moment shows that when he read the public mood better than David Cameron over phone hacking, the public responded well. Ed can lead and win an argument
  • The public seems to respond to strong leadership, something Ed has probably not shown enough of
  • The Government has handled issues such as welfare and health reform very badly, and a sharp Opposition should have made life much harder for the Government that it did. The Government has made many mistakes and have weaknesses
  • A serious alternative policy has been lacking to many bad Government policies. Time and time again the Government deploy the TINA (there is no alternative) argument, and only a sound policy base can deflect this argument.

I am not suggesting that polling data should create policy, but should help to devise effective strategies to best deploy your own arguments, and understand both the strengths and weaknesses of yourself and your opponents.

4 thoughts on “The Polls 2011 – A Cusum Perspective

  1. I think it would do Ed no harm at all to really come out fighting for our NHS. To be angry – passionate and believe in it . Many people are frightened for the future – jobs – the breakdown of law and order – cost of living etc but feel helpless to do anything but the most depressing thought of all is the demolition of the NHS. Labour should be screaming and I can hardly hear a whisper


  2. Pingback: Cameron’s Cuckoos | Think Left

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s