## Uses and comparison of GWSM and double GWSM in surveys

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Vendredi 11 décembre 2020
Estelle Medous
(Toulouse School of Economics, Université de Franche-Comté)

In surveys, there may be no sampling frame for the target population. A solution is to find a frame population linked in some way to the target population and use indirect sampling to draw a sample in the target population. The sampling weights of the sampled units can be determined using the General Weight Share Method (GWSM). This method cannot be applied when some of the links between the frame population and the sample in the target population are missing. A solution to avoid this issue is to consider an intermediate population linked in some way to both the frame and target populations. Then the GWSM can be used twice, first between the frame and intermediate populations and then between the intermediate and target populations. As illustrated with the French postal traffic survey, this double GWSM appears to be deteriorating the precision of estimators in some situations. Mathematical expressions for the loss of precision can be derived exactly for some sampling designs such as Poisson sampling or Simple Random Sampling Without Replacement. Using these mathematical expressions, it is possible to highlight the magnitude of the loss of precision in some practical situations.