Russel-Research-Method-in-Anthropology

152 Chapter 6
attracts a slightly more affluent group of buyers. If you do a systematic sample
of every 10th apartment then, depending on where you entered the list of
apartments, you’d have a sample of 180 corner apartments or no corner apartments
at all.
David and Mary Hatch (1947) studied the Sunday society pages of the New
York Times for the years 1932–1942. They found only stories about weddings
of Protestants and concluded that the elite of New York must therefore be Protestant.
Cahnman (1948) pointed out that the Hatches had studied only June
issues of the Times. It seemed reasonable. After all, aren’t most society weddings
in June? Well, yes. Protestant weddings. Upper-class Jews married in
other months, and the Times covered those weddings as well.
You can avoid the periodicity problem by doing simple random sampling,
but if that’s not possible, another solution is to make two systematic passes
through the population using different sampling intervals. Then you can compare
the two samples. Any differences should be attributable to sampling
error. If they’re not, then you might have a periodicity problem.
Sampling from a Telephone Book
Systematic sampling is fine if you know that the sampling frame has 48,673
elements. What do you do when the size of the sampling frame is unknown?
A big telephone book is an unnumbered sampling frame of unknown size. To
use this kind of sampling frame, first determine the number of pages that actually
contain listings. To do this, jot down the number of the first and last pages
on which listings appear. Most phone books begin with a lot of pages that do
not contain listings.
Suppose the listings begin on page 30 and end on page 520. Subtract 30
from 520 and add 1 (520 – 30 1 491) to calculate the number of pages
that carry listings.
Then note the number of columns per page and the number of lines per
column (count all the lines in a column, even the blank ones).
Suppose the phone book has three columns and 96 lines per column (this is
quite typical). To take a random sample of 200 nonbusiness listings from this
phone book, take a random sample of 400 page numbers (yes, 400) out of the
491 page numbers between 30 and 520. Just think of the pages as a numbered
sampling frame of 491 elements. Next, take a sample of 400 column numbers.
Since there are three columns, you want 400 random choices of the numbers
1, 2, 3. Finally, take a sample of 400 line numbers. Since there are 96 lines,
you want 400 random numbers between 1 and 96.
Match up the three sets of numbers and pick the sample of listings in the
phone book. If the first random number between 30 and 520 is 116, go to page