## Technote (FAQ)

## Question

Please define "Case weight" and "Frequency" as presented in the Model Definition step (Step 2) of the Tree Wizard in Answer Tree.

## Answer

"Frequency" indicates the variable that specifies frequencies for cases, if any. Use this if records in your data set represent more than one unit - for example, if you are analyzing aggregated data. Values for a frequency variable should be positive integers. Cases with negative or zero frequency weights are excluded from the analysis. Non-integer frequency values are rounded to the nearest integer. The frequency variable should be the variable that you would refer to as a weight variable in SPSS (in the Data->Weight Cases menu).

"Case Weight" indicates the variable that specifies case weights, if any. Case weights are used to account for differences in variance across levels of the target variable (heteroscedasticity). These weights are used in model estimation but DO NOT affect cell frequencies. Case weight values should be positive, but they can be fractional. Cases with negative or zero case weight are excluded from the analysis. With a categorical dependent variable, cases that belong to the same dependent variable class and the same predictor variable are grouped together as a cell. The corresponding case weights

are aggregated to form a cell weight for that cell. A contingency table, in which classes of the dependent variable are used as columns and categories of the predictor variable being studied are used as rows, is formed and cell weights are used in the analysis. Case weights are ignored when using the QUEST growing method.