Desktop User Guides > Professional > Data management scripting > Working with the Weight component > General weighting options
General weighting options
This topic describes various options that you can apply when you are using any of the three weighting methods. The rim weighting method has some additional options. For further information, see Rim weighting options.
Weighting to a specified total
By default the Weight component calculates the weights for each respondent as follows:
If target weighting is selected, the weighted total equals the sum of the targets defined in the weighting matrix.
If factor weighting is selected, the weighted total equals the sum of the counts multiplied by the factors in all of the cells in the weighting matrix.
If rim weighting is selected, the weighted total equals the sum of the targets given for the first variable specified.
However, you can change this behavior as follows:
If you want the weighted total to equal the unweighted total, set the Weight.TotalType property to 2.
If you want to define the weighted total, set the Weight.TotalType property to 3 and specify the weighted total in the Weight.WeightedTotal property.
You can optionally specify a numeric variable to use as a preweight. The Weight component then applies the weighting defined in this variable to the data before performing the weighting calculations. You specify the name of the preweight variable to use in the Weight.PreweightVariable property.
When performing factor and target weighting, the preweight is applied before the weighting calculations. However, when using rim weighting, the preweight is applied after the rim weighting and the minimum/maximum weight adjustments.
Preweights are often used in studies that deal with opinions and in which, for example, an adult male respondent is counted as the total number of male adults in his household. The theory behind this is that generally all of the adult males in a household have similar opinions. Another use is in CATI political polls where a respondent is preweighted by the number of calls it took to reach them. The supposition behind this is that the more calls it takes to reach a respondent, the more people there are like them, who are equally hard to reach. The respondent is therefore preweighted in order to represent the many similar respondents who are never interviewed.
Postweights are the opposite of preweights. Postweights are applied after all of the other weighting has been applied. Postweights therefore have no effect on the way in which the weighting targets are reached. You specify the name of the numeric variable to use for postweighting in the Weight.PostweightVariable property.
Postweights are generally used to make a final adjustment to a specific item. For example, when a survey is conducted in London and Inverness and 200 respondents are interviewed in each city. Target weighting is calculated to balance each group according to gender and age so that the samples match the patterns of the total populations in those cities. After this is done, you might apply a postweight to adjust the totals for each city into their correct relative proportions, where London has a much larger population than Inverness.
Minimum and maximum weights
You can define the minimum and maximum weights that you want to apply by using the Weight.MinWeight and Weight.MaxWeight properties. When you use either or both of these options, you can specify the maximum number of iterations that the Weight component is to make when attempting to fit the minimum and/or maximum weights to the data. You do this using the Weight.MinMaxIterations property. (This property is unrelated to the Weight.RimIterations property, which applies to only rim weighting.)
You can use this feature with target, factor, input, and rim weighting. Use it with care: if minimum or maximum adjustment occurs, it is possible that the targets or proportions defined in the matrix are not met.
When you specify MinWeight or MaxWeight, the Weight component tries to ensure that the maximum or minimum weights used in the table match your specifications. It component performs the weighting calculations and adjustments as follows:
1 Calculate the weight for each cell of the table.
2 Compare each weight against the minimum and maximum values defined.
If a weight is less than the minimum value, it is set to the minimum value; if it is more than the maximum value, it is set to the maximum value.
3 If no adjustment is necessary, the weighting calculation is complete.
If adjustments were necessary, the Weight component calculates the total obtained using the modified weights, and then compares it with the total obtained using the unmodified weights.
If the totals are different, the Weight component adjusts the weights which were not set to MaxWeight or MinWeight, and then returns to step 2.
If all weights are set to MaxWeight or MinWeight, so that no correction is possible, the Weight component uses the original values.
All adjustments made with this type of weighting are recorded in the weighting report (see Weighting report).
Preweights or postweights are not affected by adjustments made by this stage of the weighting process.
Excluding cases
You can exclude respondents from a weighting calculation by defining a filter. For an example of doing this, see More on target weighting.
Working with the Weight component