# Define a Multidimensional Unfolding Model

The Model dialog box allows you to specify a scaling model, its minimum and maximum number of dimensions, the structure of the proximity matrix, the transformation to use on the proximities, and whether proximities are transformed conditonal upon the row, conditional upon the source, or unconditionally on the source.

Scaling Model. Choose from the following alternatives:

• Identity. All sources have the same configuration.
• Weighted Euclidean. This model is an individual differences model. Each source has an individual space in which every dimension of the common space is weighted differentially.
• Generalized Euclidean. This model is an individual differences model. Each source has an individual space that is equal to a rotation of the common space, followed by a differential weighting of the dimensions.

Proximities. Specify whether your proximity matrix contains measures of similarity or dissimilarity.

Dimensions. By default, a solution is computed in two dimensions (Minimum = 2, Maximum = 2). You can choose an integer minimum and maximum from 1 to the number of objects minus 1 as long as the minimum is less than or equal to the maximum. The procedure computes a solution in the maximum dimensionality and then reduces the dimensionality in steps until the lowest is reached.

Proximity Transformations. Choose from the following alternatives:

• None. The proximities are not transformed. You can optionally select Include intercept, in which case the proximities can be shifted by a constant term.
• Linear. The transformed proximities are proportional to the original proximities; that is, the transformation function estimates a slope and the intercept is fixed at 0. This is also called a ratio transformation. You can optionally select Include intercept, in which case the proximities can also be shifted by a constant term. This is also called an interval transformation.
• Spline. The transformed proximities are a smooth nondecreasing piecewise polynomial transformation of the original proximities. You can specify the degree of the polynomial and the number of interior knots. You can optionally select Include intercept, in which case the proximities can also be shifted by a constant term.
• Smooth. The transformed proximities have the same order as the original proximities, including a restriction that takes the differences between subsequent values into account. The result is a "smooth ordinal" transformation. You can specify whether tied proximities should be kept tied or allowed to become untied.
• Ordinal. The transformed proximities have the same order as the original proximities. You can specify whether tied proximities should be kept tied or allowed to become untied.

Apply Transformations. Specify whether only proximities within each row are compared with each other, or only proximities within each source are compared with each other, or the comparisons are unconditional on the row or source; that is, whether the transformations are performed per row, per source, or over all proximities at once.

To Define a Multidimensional Unfolding Model

This feature requires the Categories option.