swallow does not make a summer”. In the popular phrase it involves leaping to
a conclusion.
Biased Sample
A biased sample is one that is falsely taken to be typical of a population from
which it is drawn. This error can occur because the means of obtaining the
sample attract one particular type more than another. For example, phone-in
polls on radio are susceptible to this error because the respondents are self-
selected. People who care most about an issue are more likely to respond than
others.
A famous example of this error occrurred in 1936, in the early days of opinion
polling. The American Literary Digest
magazine performed a random
telephone poll of two million people asking them their voting preferences in the
forthcoming election. They got it wrong because their sample was biased. At
the time, only some households had telephones, and telephone owners were
not a good sample of the electorate as a whole.
159
___________________
159
In contrast, a poll of only 50,000 citizens selected by George
Gallup's organisation successfully predicted the result, leading to the
popularity of the Gallup poll.
 |
 |
 |