All surveys have problems. In this case, "Is that guy obese, or did he have bad posture/scoliosis so was sticking his belly out?" It gets worse when the medical definition a few years ago was forced to leave the old height-weight charts, and then came up with the "new" body mass index charts that are basically the old height weight charts renamed and do not address percent body fat and physical condition. I once knew a Navy machinist mate who was a weight lifter and was probably under 5% body fat, and he was required to go on a diet because his body mass index was obese. At least as important as the survey or measurement itself is the criteria or metric in use. If obese means 210 pounds at 6 feet tall, there are a lot of people who are not "fat" who will be branded obese. Sadly, that is also used as an excuse by health insurance companies to raise rates.
Even when the real survey is rigorous and statistically sound, journalists will boil out the goodness before serving up to their readership.
Percentages are useless metrics unless accompanied by confidence intervals etc, yet journalists will routinely drop these from their articles because their readership don't understand the relevance.
A change from 40% to 45% might or might not be statistically relevant, but that is all most reporters will focus on.
Even ignoring the statistical errors and other mathematical issues, some surveys are crafted to get the desired answers. I recall humoring a telephone survey once (never again) and listening to the questions it became quite apparent to me that the questions were worded in such a way to get a specific answer. After about the third or fourth question, I told the person on the other end of the line that this survey was male bovine excrement (but I used the more familiar term), and that these questions were simply rigged to get a desired answer and I hung up. They didn't want people's opinion or position, they wanted cleverly fabricated data to "support" their a priori position.
Too many people lack statistical savvy, so these surveys don't get the belly laughs they deserve. Language skills today are poor too. Many reporters illogically think that to "beg the question" means to ask for an answer. (If you think do too, see http://en.wikipedia.org/wiki/Begging_the_question. An air-conditioner technician wanted to replace a 1/3-hp motor with a 1/4-hp one (probably all he had in the truck) and justified its adequacy by stating that four is bigger than three, so it was even more powerful. Either he believed that or he hoped the customer would. She threw him out.
I sometimes use a humorously wrong word and so do you. What does "impugn too much precision" mean? Did you mean "impute"?
The public suffers from what scientist Douglas R Hofstadter called "innumeracy", later popularized in a book of the same name by mathematician John Allen Paulos (see http://www.innumeracy.com/).
And it has gotten worse, even basic calculations such as making change are now done "automatically" by the cash register--or if the purchase is by credit/debit card, there is no change to figure, anyway.
With the danger of sounding elitist, I think the underlying problem is that the wider public and certainly the media has a very poor understanding of stastics, probabilities and scientific concepts.
Good engineers and scientists have an understanding and appreciation for subtleties, probabilities and degrees of things. For example, something is found to be n% with a 95% confidence level. The average person just wants a simple answer.
Let's take a hotly debated issue, like global warming. There have been a lot of studies, the overwhelming majority of which reported a high probability of warming global climate.
Then, the debate started, with lobby groups on both sides with vested interests. Some media folks had the misguided belief that you have to give equal weight to both sides in the debate, even if it took digging up some pseudo-scientific opinions and most often they did not have the capacity of distinguishing good studies from bad ones. Some of the counterarguments were also spurious, like saying that "this year, where I live, we had an unusually cold winter so where is your global warming now?"
Then, there is the question of if it's happening, what should be done about it or should anything be done, at all? ...but let's not go there!
Once I heard an interview with a climate scientist who tried to rationally explain the details and also the uncertainties of the modeling and how to evaluate the collected data. The arguments were quite compelling about warming global temperatures and rising sea levels but what the interviewer took away was that since we can't say with 100% certainty that sea levels will rise x feet/metres by year y, it probably won't be happening at all.
So, opinions flourished with religious fervour at the extreme ends of the scale, which suited the media perfectly - that's what sells papers and gives pageviews and airtime.
Meanwhile, the average person would listen to this and ask: "So, is it happening or not?!"
Sorry, just "looking" doesn't tell you if they are obese--just "large": as someone noted above, the 250-pound/all muscle/no fat footballer is not obese, but sure is big. You need to know their weight (mass) to set a body mass index. But you are right about that last comment--do people even give the right answers? Do they "fudge" to sound better, or maybe they don't know, so they make something upo?
It would be simple to take a fairly accurate survey for obese people, just watch and count them on the sidewalk. The downside is it would only represent the folks on that sidewalk, heading to the pizza places or whatever. IT seems like a lot of surveys are not nearly that well organized, and I am certain that many are just plain made up-numbers pulled from thin air. But I never believe any surveys so it does not bother me much. Also, when they call on the phone, do they really think they are getting right answers?