why are pilot studies used?
A pilot experiment/study is often used to test the design of the full-scale experiment which then can be adjusted. It is a potentially valuable insight and should anything be missing in the pilot study it can be added to the full-scale (and more expensive) experiment to improve the chances of a clear outcome.
For a pilot test, surveyors typically contact a large number of people so that potential differences within and across groups in the population can be analyzed. In addition, pilot tests for many surveys test the full implementation procedures (e.g., contact letters, incentives, callbacks, etc.).