Asking Questions - The Definitive Guide To Questionnaire Design ...

66 ASKING QUESTIONS
calendar year, even if they are unable to remember the details of
how or why the money was spent or obtained. The best explanation
of this is that they obtained summary information for another
purpose, such as tax records, or because they budgeted a specified
amount of money for a vacation.
If summary information is likely to be available from records
and is all that is required, you should use that information instead
of taking data for a much shorter time period and calculating the
yearly amount. Ordinarily, however, you will be interested in both
the summary data and the details of individual events. In this case,
both summary questions and detailed questions for a short time
period should be asked. Comparing the summary results with those
obtained from extrapolating the data from the shorter period allows
you to check the reliability of responses.
How to Minimize Telescoping. An appropriate time period is also
important if you are to minimize backward telescoping, or remembering
events as happening more recently than they did. Suppose
that a national sample of households are asked to report the amount
of coffee they purchased in the past seven days and that this total is
then compared with shipments of all coffee manufacturers or observed
sales in retail outlets. These comparisons usually show that
the amount reported is more than 50 percent higher than the
amount manufactured and sold. What is happening is a process
called telescoping.
Telescoping results when the respondent remembers that the
event occurred but forgets the exact date. In the past, most researchers
were not concerned about telescoping because they
believed that errors in the dates would be randomly distributed
around the true date. However, recent research indicates that, as
time passes, respondents are more uncertain about dates. As a
result, respondents typically round their answers to conventional
time periods, such as ten days ago, one month ago, or three months
ago. The result of these two processes is to produce an overstatement
of the reported events. Thus, an overstatement of coffee pur-