Double sampling - ARCHIVED

The theory of double sampling is usually presented under the assumption that one of the samples is nested within the other. This type of sampling is called two-phase sampling. The first-phase sample provides auxiliary information (x) that is relatively inexpensive to obtain, whereas the second-phase sample: (b) to improve the estimate using a difference, ratio or regression estimator; or (c) to draw a sub-sample of non-respondent units. However, it is not necessary for one of the samples to be nested in the other or selected from the same frame. The case of non-nested double sampling is dealt with in passing in the classical works on sampling (Des Raj 1968, Cochrane 1977). This method is now used in several national statistical agencies. This paper consolidates double sampling by presenting it in a unified manner. Several examples of surveys used at Statistics Canada illustrate this unification.