Why were the exit polls so wrong about Rena?

Elias Nicolakopoulos: “The people who were willing to respond about their vote were mostly SYRIZA voters” – “The ones who voted for the government were not willing to respond – “Golden Dawn has demonstrated its power in the local elections. It is here to stay” – “Polls before municipal elections can only reveal a general trend…”

“We made a mistake with Dourou, all the deviations from the candidates with smaller percentages were added to her percentage” said Elias Nicolakopoulos, moderator of last night’s exit polls, commenting on the misleading results for voting estimates that were announced seconds after the polls closed in the first round of local elections.
Focusing on the big lead the exit polls showed for Mrs. Rena Dourou in Attica region and for the candidate of SYRIZA Gavriil Sakellaridis in the Municipality of Athens, Mr. Nicolakopoulos admitted that in both cases the final percentages were too high in the first estimate, but attributed this fact to the behavior of the voters.

More specifically, he said that those who voted for the government chose not to respond to exit polls, while the SYRIZA voters were willing to share their choice when asked by polling companies.
Mr. Nicolakopoulos also admitted that the factor of misleading answers is impossible to control, but stressed that regarding last night’s exit polls, the “failure” was limited to the case of Mrs. Dourou, as the estimates for the other candidates percentages were “right on target”, for example the percentage of Mr. Koumoutsakos or Mr. Panayiotaros.

Therefore “there was no systemic error” but rather an “overestimation of Mrs. Dourou’s percentage”, added Mr. Nicolakopoulos.
Asked about the poll results of the previous weeks and the fact that they were completely “off the mark”, Mr. Nicolakopoulos stressed that “polls before municipal elections can never be completely accurate. They can only reveal a general trend.”
Finally, asked whether an exit poll will be held next Sunday, Mr. Nicolakopoulos said that there will be an exit poll for the Attica region in the second round of local elections and of course an exit poll for the European elections.
In any case, the picture described by Mr. Nikokalopoulos was mirrored by last night’s events. There was an official statement from SYRIZA, minutes after the polls closed, which spoke of “a clear defeat of the government,” a statement that finally provides a measure of the difference between exit polls and reality. Because when the first surveys held at the polling stations placed Ms. Dourou at 29% and Mr Sgouros at 22.5%, the celebrations of the party seemed entirely justified. However, these percentages were only a rough estimate, communicated through the media at 19:00 on Sunday.
Approximately 12 hours later, after almost 100% of the votes have been counted, the celebrations for the alleged triumphs have been limited to a post-election disource of “trends” and “messages”. In the example above, the estimated lead of 6.5 units which the exit polls gave Ms. Dourou turned out to be meager 1.6% lead, as the results in Attica are now 23.71% for the candidate of SYRIZA and 22.13 % for her opponent.