Turkish elections: How to explain the anomalous fingerprints

Question

On 14th of May, millions of Turkish voters went to the polls to cast their votes in the parliamentary elections. Recently, the official results were published in the website of the Supreme Election Council.

As a data science enthusiast, I decided to download the results and play with them. There is a 2012 paper that suggested to plot the histogram of voter turnout against the votes that the winning party got for each ballot. Namely, for each ballot, we compute the voter turnout, obtained by

and we consider what ratio of voters voted for the winning party

The paper suggests that the histogram should look 'unimodal'. Unimodal means that there is a single mode of the data, that is, there is a single voting behaviour around which all ballots are concentrated, within a certain margin of error. As an example, we might see that most of the ballots have similar turnouts, say %90 and similar percentages for the winning party, say, %40. Otherwise, the authors argue, the results can be considered anomalous (possibly due to fraud, or some other explanations).

The following is the fingerprint (the term used in the aforementioned paper) of the whole election. Each ballot contains a number of votes between 10 and 400. The x-axis is the turnout, the y-axis is the votes for the winning party (namely, AKP). The colors reflect the number of ballots with the same xy-coordinates. Dark colors mean that there is a small number of ballots in that box and the light colors mean there is a big number of ballots in the box.

As you can see from the plot, the voter turnout is concentrated around %90 because that is where most of the light colors are. AKP got approximately %35 of the votes and the plot is slightly smeared, between %10 and %50.

This plot certainly looks unimodal, since all light colors are close to each other and connected.

Then I considered the fingerprints of the election results of 4 cities, the 3 cities with highest population, Istanbul, Ankara and Izmir and the city that was recently affected by a major earthquake, Hatay. Namely, for each city, we only consider the ballots in that city and we plot the voter turnout and the votes for the winning party, just like we did for the whole election.

One can see that Istanbul and Izmir have unimodal plots, indeed Istanbul looks almost the same as the fingerprint of the whole election. Izmir looks also similar the the first fingerprint, however it is translated down, the ballots are concentrated around %20 for AKP.

On the other hand, Ankara and Hatay look different: their fingerprints are bimodal, i.e., have two modes. Ballots in Ankara are concentrated around two percentages, %20 for AKP and %40 for AKP. Hatay's fingerprint is also bimodal, there is concentration around <%10 for AKP and >%40 for AKP.

This is what I want to understand.

What are the possible explanations for the election fingerprint of Ankara and Hatay to look bimodal whereas Istanbul and Izmir don't?

Disclaimer: Some commentators suggested that the question might lead some people to jump to controversial conclusions. I don't think the data above suggests fraud in Turkish elections. There is a myriad of possible explanations for the fingerprints above and these reasons are what I am looking for.

Answer 1

What are the possible explanations for the election fingerprint of Ankara and Hatay to look bimodal whereas Istanbul and Izmir don't?

There are parts of each city that strongly favor one party, and different parts of each city that far less strongly favor that party.

You would expect this in cities with strong political divisions into discrete political identity clusters along geographic lines.

You see the same thing, for example, in Denver municipal elections, where mostly Hispanic neighborhoods, mostly black neighborhoods, and mostly white neighborhoods tend to favor different candidates despite all neighborhoods having generally similar turnouts. Due to a history of residential segregation in the city, those divides are quite stark and not gradual, leading to bimodal or trimodal distributions.

Comments to the post rightly suggest that you'd expect something similar in cities like Belfast and Jerusalem that are famous for their stark ethnic/religious divisions that are geographically organized. Beirut would be another example.

Comments to this post also indicate that at least one of the cities in question is known to follow this pattern:

Hatay is a peculiar part of Turkey (annexed from French Syria in 1938). It was affected by the earthquake, which may have effects on turnout. But more significantly the AKP appeals primarily to pious Turks following Sunni Islam; there are some villages like that in Hatay with a mix of pious and secular Turks, but many other groups exist and dominate other villages, including a large number of Arabic speakers and their Turkish speaking descendents who follow Alawite Islam, as well as other ethnic and religious groups, which may explain a number of places giving almost no votes to the AKP. – Henry

@Henry This is a very interesting point. I also checked the cities with considerable Alewite population. Two of them (Çorum and Erzincan) had similar bimodal histograms.