Developmental psychology.pdf

38 Background and Methods
*l was on the staff of the school
paper and proposed that we run a
survey on the popularity of the
three school presidential
candidates. RM, a junior, was
chosen to ask 200 out of the 1400
students attending WHS which
candidate they preferred, and
results predicted an overwhelming
victory for Louie, with Sam placing
a distant second, and Melissa an
almost nonexistent third. We
published the survey the day before
the voting began.
Two days later our staff was
rather surprised! Sam, "the surfer,"
won; Melissa, "the hood," placed a
close second; and Louie, "the
intellectual," was a close third. We
asked RM how he could have
gotten such incorrect results by
running around school asking
anyone he saw how he or she
planned to vote. He said that he felt
too sick the day of the survey to
wander all over school, so he just
asked the people in each of his
seven classes.
RM's classes consisted of
honors history, honors English,
advanced algebra, advanced
biology, chemistry, fourth-year
German, and physical education.
No wonder his sample predicted a
huge* victory for "the
intellectual". . . .
Incidental Sample An event on March. 1, 1932, some time between 8 and 10 P.M.,
illustrates the problem of nonrandom sampling. Someone entered a baby's bedroom
and fled into the night with the twenty-month-old son of Charles and Anne Morrow
Lindbergh, a kidnapping that became a national crisis. "Clues" arrived from all over
the country, and amid this concern two psychologists published an advertisement for
clairvoyant dreams about what had happened. Clairvoyance, an alleged aspect of
extrasensory perception, is the capacity to know about events without using the known
sensory capacities. There were no restrictions on who could participate, and by this
advertisement, which other newspapers picked up, more than 1,300 accounts of dreams
were received.
This procedure is called an incidental sample because anyone who happens to
respond is included. There is no effort to question people of certain ages, both sexes,
and various occupational and ethnic groups. Incidental samples are common in survey
research because they are easy to obtain.
When the baby's body was discovered, all of the dreams were examined for
accuracy of information. To make these studies as objective as possible, the psychologists
focused on only three incontestable facts: the baby was found dead, it was in a
shallow grave, and it was near the woods. Analyses showed that only four dreams reported
these items correctly, a figure that is extremely low because the baby would
have to be (a) dead or alive, (b) above ground, in the ground, or in the water and, if
in the ground, (c) in the cellar of a building, in an open area, or in the woods. Many
more correct dreams would be expected just on the basis of chance. With less than 1
percent correct, there was no evidence for clairvoyant dreams, and the question of who
did the kidnapping is still debated (Murray & Wheeler, 1937).
The chief limitation in this incidental sample, like all others, is that not everyone
in the population had an equal opportunity to participate. The advertisement was
carried only in large city newspapers. Many people in small towns might have had
clairvoyant dreams, but they were not included. This lack of people from small towns
may or may not have been critical, for there is no clear evidence that the incidence of
clairvoyance is higher in rural as opposed to urban areas.*
Interpreting Results
The nature of the sample determines the overall value of any survey research. When
the sample is not representative, the investigator cannot with any confidence draw conclusions
about the larger population. There is considerable concern about this problem
in survey research, especially when members of the sample do not return the questionnaires,
inventories, and other attempts to gather data (Rudd & Maxwell, 1980;
Sosdian & Sharp, 1980).
Limits in Generalizing In one instance an anthropologist studied the dreams of
people living in Tzintzuntzan, a small Mexican village. The sample included 16 men
and 26 women, a sex ratio that did not approximate the 50-50 distribution found in
such communities. Each villager apparently did not have an equal chance of being
chosen, and in fact the investigator states that he essentially studied his friends. Of
the 334 dreams collected, two men and three women contributed more than one-third
of the males' and females' dreams, respectively.
The researcher concluded that the dreams reflected the basic character and
cultural outlook of the village. It should have been concluded that the dreams reflected
the outlook of an incidental sample, especially the researcher's friends in Tzintzuntzan.
These people may not have been representative of the village as a whole (Foster, 1973).
Limits of Verbal Reports A further limitation in survey research is that the
investigator observes only the marks on a questionnaire or inventory rather than the
behavior itself. Survey data indicate what people say about their dreams, favorite cereal,