Studying Cities and City Life by Mark Abrahamson

Author:Mark Abrahamson [Abrahamson, Mark]
Language: eng
Format: epub
ISBN: 9780415738019
Google: xCQmswEACAAJ
Publisher: Routledge
Published: 2016-01-15T03:24:46+00:00

Cross-sectional and longitudinal studies

A second basic distinction between types of samples concerns whether elements are observed or questioned only at one point in time – a cross-sectional study; or whether the same elements are observed or questioned over an extended period of time – a longitudinal study.

The typical sample survey takes a stop action picture of a cross-section of a population at one point in time. It is analogous to a photograph. With a cross-sectional survey it is important to complete the data collection as quickly as possible because the longer the time period involved, the greater the possibility that changes will occur in the population, and that will increase variability, which we have previously seen to increase the size of C.I.s. To pursue the analogy, lengthening the time frame of data collection in a cross-sectional sample survey can be likened to over-exposing a photograph by leaving the shutter of the camera open too long. In the following discussion of probability samples, cross-sectional designs are assumed unless stated to the contrary.

In order to analyze change when relying upon cross-sectional studies, it is necessary to examine a series of such studies, arranged chronologically. Because such trend analyses typically involve analyzing previously collected data, trend studies are discussed in Chapter 6, with other types of secondary data analysis. The only type of longitudinal study that always involves primary data collection is a panel study, and it is discussed later in this chapter.

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