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I am reading a book on sampling. I don't understand this sentence:

How many interviews do you suppose it took each of these pollsters to come within a few percentage points in estimating the behavior of about a hundred million voters? Fewer than 2000!

If you need more context to help, please ask :)

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  • They figured out how the entire population of a country would vote in an upcoming election by asking only 2000 people a few questions. Another example: if you pick a random number between 1 and 1,000,000, and kept it secret I guarantee I could guess it by asking you 20 questions, or fewer.
    – Dan Bron
    Oct 2, 2015 at 17:15
  • I have the exact same problem when listening to politicians.
    – Hot Licks
    Oct 2, 2015 at 17:19
  • @HotLicks Solution: don't listen to politicians.
    – Dan Bron
    Oct 2, 2015 at 17:24
  • I now understand this sentence with your help and explanation. I could guess from the context what it probably means. But could you kindly explain how you get at the meaning? @DanBron
    – k.k.
    Oct 2, 2015 at 17:27
  • @k.k. I'm afraid I can't :( That's like someone asking you how you can wiggle your fingers or stand on two feet: you just can. I've been using English my whole life, at this point the mechanisms of it are invisible to me.
    – Dan Bron
    Oct 2, 2015 at 17:30

2 Answers 2

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So ignoring the meanings of the words, let's just rearrange them. You started with:

How many interviews do you suppose it took each of these pollsters to come within a few percentage points in estimating the behavior of about a hundred million voters? Fewer than 2000!

Written more simply it says:

Pollsters can come within a few percentage points in estimating the behavior of about a hundred million voters with fewer than 2000 interviews.

There is a set phrase in there:

come within a few percentage points

means that, should they estimate 35% of voters will vote for X, reality will turn out to be no less than 33% and no more than 38%. "A few" isn't superprecise, but if reality was 9% or 90% then the pollster wouldn't have come wthin a few percentage points.

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  • great! "come within a few percentage points", this is the exact point I am confused about. My instinct tells me that the doer of the action "come" in this case should be a figure or a datum, but in the arranged sentence, the doer turns out to be people "pollsters". So is it correct? @Kate Gregory
    – k.k.
    Oct 8, 2015 at 9:58
  • Yes, the subject is pollsters, They are performing the action of predicting election results. If the predictions turn out to be close to reality, we might say they "came close" to reality, or "came within" a certain distance of it. Oct 8, 2015 at 10:12
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Unless you are familar with Statistics as a discipline, it would be very difficult for you to understand the sentence.

Especially, you have to know what "standard deviation" and "sampling error" mean.

For example (very simplified)

If there is an election poll and A candidate is expected to get 45% of the votes with confidence level of 95% and sampling error of +/- 3 percentage points, it means;

If polls on the candidate are conducted 100 times, A candidate will get 42% to 48% of the votes in 95 times out of 100 times.

The sentence means you can just ask not more than 2,000 people out of 1 million people to come up with a forecast of an election result within the set "confidence level" & "sample errors (here within a few percentage points)".

As you can easily guess, the more samples you have, the closer a poll results will become. But not 100% necessarily as it will cost more money and time.

If I rephrase it for you to understand it more easily in a declarative sentence instead of an interrogative sentence;

It took fewer than 2,000 interviews (number of samples) for each of these pollsters to come within a few percentage points (sampling error) in estimating the behavior (election result forecast) of about a hundred million voters.

Please note that it is a very simplified explanation.

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  • a more in-depth explanation. My problem sticks to the surface. I know specialized knowledge helps me understand the sentence more precisely. To put it simple, my problem is I don't get at why the sentence is arranged in this way to express the meaning it is supposed to. I understand each word @Rathony
    – k.k.
    Oct 2, 2015 at 18:06
  • @k.k. The sentence is constructed for people who understand both English and Statistics. There is nothing wrong with the sentence if you understand both of them.
    – user140086
    Oct 2, 2015 at 18:08
  • @k.k. Take a look at the rephrased sentence in the answer. It will be easier for you to understand the structure.
    – user140086
    Oct 2, 2015 at 18:13

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