Friday, November 5, 2010

What is a significant change of opinion?

I am puzzled by something. Suppose I ask five people if they prefer tea or coffee? Three say coffee, two say tea. Four years later I ask them again. One of the five people has changed their mind, now two prefer coffee and three tea. Suppose the sample size is much larger, but still only one in five people change their preference. I would not say there was a "massive swing" in preference or that drinks "preference did an almost complete turnabout".

Furthermore, suppose also that those five people had all previously said they did not wish to register as having a definite opinion on their preference. Then it should hardly be surprising if one in five changed their opinion.

Hence, I am puzzled by an article in the Wall Street Journal by Gerald F. Seib, Unaligned votes tilt rightward en masse. It states:

A massive swing by independent voters propelled the Republican Party to a series of key victories.... 
In House races nationally, Republicans won the votes of independents—voters who said they aren't affiliated with any party—by a 55% to 40% margin, a compilation of exit polls from across the country showed.
In other words, independents' preference did an almost complete turnabout over the last four years: They favored Democrats by 18 points then, Republicans by 15 points Tuesday.


  1. Surely to answer the question in your title you need data. Specifically, you need to know how large swings are in typical elections. I don't have the data to hand but I'm pretty confident that this was a very large swing.

    Further, you need to remember that this is a first past the post system so small swings in percentages will tend to be amplified onto large swings in numbers of congressmen/MPs etc.

  2. Hi Ben
    Thanks for your comment.
    Indeed this swing is larger than in a typical election.
    It is also true that small swings in percentages are amplified in changes in numbers of MPs.
    However, the point I was trying to make still remains. Perhaps I am just being too picky about language.
    To me "an almost complete turnabout" in preference means that more than 80 per cent of people changed their mind not less than 20 per cent.