SVWEIGHT procedure

Forms survey weights (S.D. Langton).


Options

PRINT = string
Controls printed output (summary, stratumsummary, psusummary); default summ, stra, psus

PLOT = string
Controls which high-resolution graphs are plotted (weights); default * i.e. none

STRATUMFACTOR = factor
Stratification factor; default *, i.e. unstratified

NUNITS = tables, scalars or variates
Numbers of units in each STRATUMFACTOR (for a multistage design these will be the number of primary sampling units)

SAMPLINGUNITS = factor
Factor indicating the primary sampling units; default *, i.e. single stage design.

NSECONDARYUNITS = tables, scalars or variates
Numbers of secondary sampling units for each level of the SAMPLINGUNITS factor


Parameters

Y = variates or scalars
Response data or a scalar indicating the number of sampled units

OUTWEIGHTS = variates
Saves weights


Description

SVWEIGHT creates weights for surveys. The information about the numbers of sampling units in the survey population can be supplied in one of two ways.

1.       The option NUNITS can be used to list the number of primary sampling units per stratum using a table or variate with one value for each stratum. Similarly, in a two-stage design, NSECONDARYUNITS indicates the number of secondary units in each primary sampling unit.

2.       The dataset can contain the full survey population with unsampled (or non-responding) units indicated by missing values for the response variables (Y parameter). This allows GenStat to deduce the numbers of units without the need to supply any further information; it is thus simple to use, but is not feasible with large or complex surveys. The NUNITS (and NSECONDARYUNITS if appropriate) option should be set to a value of -1 to indicate that this is required.

With the first method the Y parameter can be left unset, except in the case of a simple random sample, where it must be set in order for the procedure to know the number of sampled units; in this case Y can either be set to a variate containing the responses or to a scalar containing the number of sampled units. Other information on the survey design is provided using the STRATUMFACTOR and SAMPLINGUNITS options. The OUTWEIGHTS parameter saves the variate of weights (corresponding to each response variable in the case where more than one Y variable is set).

   The PRINT option allows you to print various summaries, and you can set PLOT=weights to plot a histograms of the weights.

 

Options: PRINT, PLOT, STRATUMFACTOR, NUNITS, SAMPLINGUNITS, NSECONDARYUNITS.

Parameters: Y, OUTWEIGHTS.


Method

The procedure uses the methods for survey analysis described in most survey analysis textbooks, calculating weights as the inverse of the probabilities of inclusion (see for example, Sarndal et al. 1992).


Action with RESTRICT

Any restrictions on Y, SAMPLINGUNITS, STRATUMFACTOR or WEIGHTS are ignored.


Reference

Sarndal, C., Swenssion, B. & Wretman, J. (1992). Model Assisted Survey Sampling. Springer-Verlag, New York.