How you record your data can affect your ability to relate various elements in the data to each other. It is important to think through (in advance!) what type of analysis you intend to do, to assure that it is measured and stored in a way that will permit its retrieval later. How the data are gathered can affect its reliability and its validity (two different things). The combined effect of these two is called “sensitivity.”
Even with the advent of microcomputers, there is still an expense attached to obtaining and analyzing data. If one were to measure all of any phenomenon, there would be no need to infer anything—one would only need to observe and report. But since one can never (well, almost never) measure everything, one must select what one will measure so as to get as accurate a picture of the totality as possible. This is called sampling. There are several ways of drawing a sample, and the size of the sample you draw will determine the confidence and the significance of the results you obtain.
© 1996 A.J.Filipovitch
Revised 11 March 2005