The idea of sampling is easily absorbed. Discuss the vocabulary, especially
"population," carefully. An opinion poll such as the Gallup Poll asks individ-
ual opinions. So the units are individual persons and the variables measured
are the answers to the questions asked. But the population involves many
choices: What lower age limit? American citizens only, or all U.S. residents?
The pervasiveness of sampling is worth emphasizing by example.
Example. Everyone is familiar with those maps of world sea-routes which
indicate the volume of traffic on each route by the width of the arrow flowing
(say) out of New York across the Atlantic and dividing to reach London,
Antwerp, etc. The Oxford Economic Atlas has such a map. It was compiled
by selecting a sample of all ships listed at Lloyd's of London, the insurer of
last resort. The location on a chosen date of each ship in the sample was
ascertained and the arrows on the map were drawn accordingly.
Example. The J. D. Power company conducts two sample surveys that are
widely quoted in automobile ads. The Initial Quality Survey concerns me-
chanical problems in individual models of new cars and light utility vehicles,
such as the Chevrolet Beretta. Power randomly selects about 90,000 new car
registrations within the first 90 days of ownership soon after the new model
year begins, with results published in February. About 35% of the people
selected respond.
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