Agriculture Reference
In-Depth Information
Chapter 10
Advances in Sampling Estimation
10.1
Introduction
After collecting data, several transformation steps are needed so that they can be
used to provide stable and efficient estimates of a population
s parameters.
Statisticians devote considerable effort to their survey designs, using auxiliary
information to select a set of units that is representative of the population from
which it was selected. In other words, if the sample considers many characteristics
of the population, it will probably generate estimates very close to the true and
unknown parameters (see Chap. 6 ) .
It is desirable to use any prior knowledge in a survey. However, it is not
recommended to only use this additional information in the design phase. Several
factors could lead to include in the estimator the auxiliary information represented
by the matrix X. For example, X may change between the design, data collection,
and dissemination of results, because some additional information may be acquired.
Moreover, problems such as nonresponses may occur, and can only be measured
after data collection. It is impossible to account for these problems in the design of
the sample.
Some relevant differences among the statistical units typically used in agricul-
tural surveys should be highlighted. We do not always have information on the
position (i.e., geo-referencing) of agricultural holdings; instead it is always known
for points and segments.
When dealing with a population of agricultural holdings, the auxiliary variables
are generally size covariates arising from administrative or census data sources. As
is typical in business surveys, this population is markedly positive asymmetric
because small family-owned holdings coexist with large companies.
Spatial coordinates are one type of information that is typical of spatially
distributed populations. They are often seen as an important data source that should
be exploited. They are the key information used by GIS (see Chap. 3 ) to integrate
the survey data with other spatial information such as satellite images, land cover
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