Stat friends especially those who work for the said polling firms please help with this question.

In the past, face-to-face interviewing was viewed by US opinion research experts as an appropriate method for conducting opinion surveys. It ostensibly allowed them to select the “right” respondent to be interviewed. After major failures, however – notably, the erroneous forecast of Thomas Dewey’s victory over Harry Truman in the 1948 US presidential elections– this survey method was abandoned, so much so that reputable pollsters in the US have now discarded it altogether.
Why was this? We invite some experts to tell us why. Chava Frankfort-Nachnias and David Nachmias in Research Methods in the Social Sciences write: “The very flexibility that is the interviewer’s chief advantage leaves room for the interviewer’s personal influence and bias.”
The pollster Kenneth Warren in his book, In Defense of Public Opinion Polling, says: “The cons of door-to-door interviews far outweigh the pros…Because of the sensitivity or personal nature of some questions, interviewers, because they were placed in face-to-face situations, have admitted that they sometimes guessed or fudged responses…These problems are a major source of bias in personal interviews, causing significant contamination of the poll data.”
These methodological and practical problems, according to Warren, doomed face-to-face interviews forever. By 1980, nobody in the US wanted to pay for this type of “fatally flawed and grossly inaccurate” surveys.
This, however, seems to have had no persuasive effect on our local pollsters.
A second glaring weakness is the extensive and general use of quota sampling to create “a representative sample” of the Philippine population. In quota sampling, survey respondents are picked from different types of people (e.g. by age, sex, religion, income) and various predetermined areas (e.g. region of country, as well as urban or rural).
This method is the most familiar form of non-probability sampling. It is supposed to mirror the same proportions in the targeted survey populations, but doesn’t. And it proved to be an earth-shaking failure in 1948 after three leading US pollsters–Gallup, Roper and Crossley—erroneously called the US presidential election in favor of Dewey instead of Truman. In the United Kingdom, where it persisted, it was blamed for the failure of the pollsters to predict Prime Minister John Majors’ victory in 1992.
“Quota sampling could never work in practice,” says Professor Warren. “Not only could pollsters not know the exact demographics so they could pick a representative sample that actually reflected the proper demographical proportions, but it was naïve to think that the interviewer could manage to interview the precise people needed to fill each quota.”
Thus today, reputable US pollsters rely almost exclusively on probability random sampling to create a “representative sample,” says Warren.
Why then do local pollsters continue to use quota sampling and face-to-face interviewing for their surveys? Why haven’t they adopted probability random sampling, which has protected US opinion polls from using contaminated data?
via Mind Games And The 2010 Elections | Filipino Voices.