Public Opinion Surveys on Fluoridation May Have Upward Biasby
Daniel A. Montgomery, B.S.
May 31, 1999
There is a significant proportion of any population who avoid disagreeing with a proposition that seems popular at the time. Upward bias can be created by asking a person if they do something like read a particular magazine. A better question would be to ask them which articles they liked the best to discover whether they read the magazine at all.1 Alfred Politz waas the marketing guru who discovered the statistical fallacy of upward bias in public opinion polls.2 In the presidential election of 1948, the other pollsters were predicting that Harry Truman would loose. They were so certain that Truman would loose that some newspapers had already printed front pages with the headline that Dewey won. The upward bias problem has been recognized in the market research industry for years. Surveys of public opinion on fluoridation have not succeeded in ruling out upward bias.
The NCAHF Newsletter, an anti-alternative health propaganda sheet, reported the results of a telephone survey of 4,000 respondents in California. 71% favored fluoridation, 15% opposed fluoridation and 14% were undecided.3 Elections in California show a discrepancy with the NCAHF data. Mountain View voted 58% for fluoridation in 1998. Santa Cruz voted 50.4% against fluoridation in 1999.
In a pre-election survey in three California towns, large majorities approved of fluoridation when they were asked, "Do you have anything against drinking fluoride in the water, even though it doesn't help adults much?" The voting was substantially less favorable. A Nielson survey measured pre-election opinions on fluoridation in the East Bay Metropolitan Utility District (EBMUD) in 1978. The EBMUD water system serves Oakland and nearby cities. 64% said yes they would vote for fluoridation, 27% said no and 10% were undecided. The vote was 50.5% in favor of fluoridation.4
A survey in Portland, Oregon in 1980 found that 71% knew the official purpose of fluoridation, but, in a referendum held shortly before this survey, Portland voters had repealed a plan to fluoridate.5
A survey in Massachusetts in 1980 found that about three fourths knew the purpose of fluoridation and 60% said they favored fluoridation, but in referenda in 14 communities held between 1980 and 1983, less than 40% voted for fluoridation.6 It is easier to say yes to fluoridation as an abstract issue than to vote for it.
Bremerton, Washington voted 55% against fluoridation in 1999. Anit-fluoridation campaigns are generally underfunded. A public debate on fluoridation was televised just before the voting. This is credited with turning the outcome strongly against fluoridation. (Mountain View California Citizens for Safe Drinking Water)
Olympia, Washington voted 52.14% against fluoridation in 1998. (The Non-Fluoridaton of Olympia)
Another indication of upward bias can be inferred from a survey in the Quebec metropolitan region in 1994. Opinions about fluoridation appeared to be practically the same in the fluoridated and the non-fluoridated municipalities. In the fluoridated municipalities, 20.4% thought fluoride prevented tooth decay, 22.0% opposed fluoridation and 3.1% knew that fluoridation increases dental fluorosis. In the non-fluoridated municipalities, 19.4% thought fluoride prevented tooth decay, 18.3% opposed fluoridation and 2.0% knew that fluoridation increases dental fluorosis. However, 19.9% of those who believed their tap water was fluoridated, whether it was or not, opposed fluoridation while 34.5% of those who believed their tap water was not fluoridated, whether it was or not, opposed fluoridation.7
It is apparent, then, that the popularity of fluoridation is overrated.