According to this paper, the poll was conducted from 8:00 am to 3:00 pm on the day of the election. More than 13,000 individuals were interviewed by trained poll-takers using a paper and pencil questionnaire. The paper describes:
The poll center of TVBS collected the exit poll data and sent them to Mitofsky International by Internet at 3:38. Mitofsky International processed the data analysis and sent the result back to TVBS at 3:55, which predicted the support rates of President Chen Shui-bian (Democratic Progressive Party, DPP) and his opposition Kuomintang (KMT) challenger Lien Chan were 47% vs.53%. Since precincts in some regions, such as Taizhong, Kaohsiung, were not closed until 5:00pm, TVBS decided to delay the projection. Until 5:12pm, they projected that the supporting rates of two candidates were 47% v.s.53%. However, since the margin of difference was less than 8%, according to the principle of the projection of exit polls, they did not declare who was the winner.Note that a couple of hours before the poll counting had finished, based on returns from 80 and then 150 precincts, Mitofsky International already called the election at 50%-50% though the TVBS poll had Lien-Soong ahead 53-47. The paper notes that revisions to exit polls are common for large geographical areas. In sum, what this paper shows is that contrary to some of the propaganda floating around, the TVBS exit poll, once revised with a few early returns, showed the KMT and the DPP in a statistical dead heat.
Then TVBS sent the quick counts (real voting results) of those precincts which were sampled in the exit polls to Mitofsky International, until 5:20pm the real results of 80 precincts had been sent to U.S. At 5:36pm, based on these 80 precincts’ real counts, Mitofsky International revised the prediction as 50% vs. 50%. At 6:01 pm, they received the data from real counts of all 150 precincts sampled and confirmed the revised support rates (50% vs. 50%).
What were the problems with this poll? They are a legion. The sampling error was rather larger than in American surveys. Non-sampling errors are more important; they show a statistically detectable bias in the poll against the DPP, which accounts for its skew toward the KMT. This is probably not the result of TVBS' innate bias against the DPP but is the result of several issues outlined in the paper. For example, there is the problem of incentives for participation in the poll. Read closely:
In 2004 Taiwan presidential election exit poll, they boldly employed incentives with intent to increase the response rate. They used magnets with logo of TVBS, the sponsor of the survey, as incentives (worth about $3 each). From the aspect of advertisement of the company, it was a good way to enhance the company’s image. TVBS has a relatively neutral image among media in Taiwan, which helps it get trust from the voters.
In addition to these obvious dampeners to participation by DPP voters, the exit pollsters were forced to stand 30 meters from the polling places. It is known that in exit polls error increases significantly when distance exceeds 25 feet/8 meters. The paper does not define "polling place" but given that polls are conducted in schools and community centers where the voting booths are deep inside the building, it is likely that in practice distances were even greater than the 30 meters suggested here. For example, I stopped by the polling station in my neighborhood during the election, and non-voters were being kept outside the school, roughly 50 meters from where voting was taking place.
That last issue may explain why there are no exit polls for Taiwan elections, because under the current rules that govern access to polling stations on election days, pollsters cannot get close enough to make them reliable.
UPDATE: Mitofsky himself noted in a piece on exit polls that the student poll-takers were not well-trained:
Regrettably, bad sampling and no estimation are the rule and not the exception in emerging nations. It seems to be common practice to tabulate the results in SPSS with little or no weighting. There are other types of missteps, too. Interviewer selection and training in recent exit polls in Venezuela and Taiwan led to biased results. Recent partisan exit polls in Azerbaijan and Mexico led to deliberately distorted results._________________
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