# Distribution

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When specifying a mixture model (which is done when using **Create > Segments**) the following options are available for specifying the shape of the mixing distribution.

**Finite**Assumes that there is no variation within each class. This is the default.**Multivariate Normal – Spherical**Forces the classes to be “spherical” (i.e., with equal variances for every variable).**Multivariate Normal – Diagonal**Estimates separate variances for each variable (i.e., in the case of**Number**and**Number - Multi**questions, this is equivalent to transforming the data to z-scores).**Multivariate Normal – Block Diagonal**Permits correlation between levels of the same attribute, but not between attributes.**Multivariate Normal – Full Covariance**Permits correlations between all attributes and attribute levels.- These assumptions are ordered from most restrict to least restrictive.
**Pool variance**Constrains the variance and covariance assumptions to be common across classes. For example, if**Multivariate Normal – Spherical**and**Pool variance**are both selected, a single variance parameter is employed for the entire model.

## See also

Further reading: Market Segmentation Software