Inspired by a friend’s rant in Facebook regarding the media’s way of presenting poll results and by a public lecture of Nate Silver at LSE, where similar problems were discussed, I decided to investigate the news regarding the popularity of the largest parties in Finland. I wondered, what the polls actually say about the popularity and is that reflected in the language used in the news.
I limit my mini-investigation to the four largest parties: Social-democrats (SDP), National Coalition Party a.k.a. Kokoomus (KOK), Centre Party a.k.a. Keskusta (KESK) and True Finns Party a.k.a. Perussuomalaiset (PS), because the polls usually only give the margin of error for the largest parties. Therefore, I can only try to estimate the accuracy of popularity of these parties.
I searched for a few latest polls in the two biggest news institutions’ websites in Finland: Yle.fi (the National Broadcasting Company) and HS.fi of Helsingin Sanomat (a broadsheet with the largest number of readers). In the end I chose seven polls, conducted between December 2012 and April 2013. Yle uses Taloustutkimus and HS TNS Gallup to conduct the analysis.
The figure clearly shows that if we consider the margins of error reported by Yle and HS, most of these polls cannot distinguish, which one of these four parties is the most popular one. However, arriving to this conclusion is not easy due to four reasons:
- Margin of error is only reported for “the biggest” parties, although I couldn’t find a definition of what “the biggest parties” mean. I assume it means these four, since there is a significant gap between these and the 5th largest party popularity in all polls. In the latest HS poll (24 April 2013) the margin was not reported at all.
- Yle polls report that the results of the polls are “more accurate than what the margin of error would imply” due to calibration methods they use, but this is not explained further. Therefore, I chose to ignore this information here.
- In order to understand, what margin of error means, one has to know that it actually is a 95% confidence interval and that this interval (in simple terms) means that “we are 95% confident that the value in the total population is within this range”. In other words, if we drew an infinite number of random samples from the Finnish population and asked, which party people support, in 95/100 cases we would get an estimate within the range of 95% confidence interval. In 5/100 cases the estimate would be outside the range. The interval is reported, since as long as we don’t actually ask everyone, we cannot be entirely certain that our estimate is correct. However, we can provide information on how certain we are. Wide range implies more uncertainty than a narrow range.
- Most importantly: the way these polls are reported in the media is almost entirely inaccurate. I will elaborate this claim below.
The first poll (Yle 2 Dec 2012) was titled “Support for Centre Party in rapid increase“, which is not far from truth, since their popularity was 2.5%-points higher than in a previous poll and the margin of error was 1.4%-points. Therefore the overlap of the 95% confidence interval is marginal: the upper limit for the old poll’s estimate is 16.9% and the lower limit for this poll’s estimate is 16.6%. So, maybe their support actually has increased. Later they state that KOK is clearly the largest party, which is not the case, not at least clearly: looking at the figure we can see that the confidence intervals of KOK and SDP overlap. Therefore, the difference in their popularity might be only a coincidence (or noise) due to sampling. In another sample we might have gotten estimates presenting similar popularity for the two, or even higher percentages for SDP. The correct interpretation thus is: KOK is more popular than PS or KESK, but not significantly different from SDP. SDP seems to be more popular than PS but we’re not confident that there is a significant difference between PS and KESK or SDP and KESK.
The reasoning for all of the polls is similar, so I won’t present it in as much detail as above for the rest of the polls. Instead I’ll focus on the most inaccurate reports I found. If you’re interested in comparing these further, please take a look at the list of links below. As long as you have fluent Finnish skills, you should be able to do it based on this blog post.
“The Centre Party is the second most popular” (HS 24 April 2013)*. Really? Looking at the figure, we quickly observe that the popularity of all four parties is really similar. We cannot even distinguish between the most and the least popular among these four — all the confidence intervals overlap. Thus, one should say: according to the latest poll, all the four biggest parties have similar levels of support.
“The Centre Party is the most popular, SDP crashed” (Yle 29 April 2013). Guess what? I don’t agree with the statement. It indeed looks like KESK is more popular than SDP, but based on these results, it is impossible to say, whether it is KESK, KOK or PS, which currently is the most popular. The estimates differ only a tiny bit and the confidence intervals clearly overlap. The statement is not just exaggerating. It is false. What about SDP then, did it crash? Well, I don’t think so. The point estimate of their popularity is indeed lower than it has been in previous Yle polls in the figure. However, we have no way of knowing, if that was due to chance (remember the sampling thing!) or if there actually is a difference, since the confidence intervals overlap in all but the earliest poll in 2 December 2012. Therefore, my interpretation of this poll is: there is little difference in popularity of KESK, KOK and PS, whereas SDP may be less popular than the three other parties and also less popular than it was in the beginning of December 2012.
Okay, the rest of the interpretations you have to conduct yourself. I’m left wondering, why false information is so commonly presented in the media. Is it due to lack of understanding of statistics? Or maybe due to a belief that people are not interested in news, which do not rank the parties? Would it be so bad to truthfully say that we don’t know, which party among certain candidates currently is the most popular? I cannot think of a reason, which justifies false statements, when the journalist clearly should know better.
* If there’s anything lost in translation, blame me, I was the one, who translated these from Finnish to English.
Links to original news articles
Margins of error:
- Yle 2 Dec ±1.4%-points
- Yle 30 Dec ±2%-points
- Yle 8 Mar ±1.3%-points
- Yle 29 Apr ±1.4%-points
- HS 23 Jan ±”less than 2″%-points –> I assumed 1.9%-points
- HS 27 Mar ±”less than 2″%-points –> I assumed 1.9%-points
- HS 24 Apr not reported –> I assumed 1.9%-points