SPSS® 12.0 Command Syntax Reference

108 ALSCAL
differences model proposed by Carroll and Chang (1970). This model can be
used only when SHAPE=ASYMMETRIC, the analysis involves more than one
data matrix, and more than one dimension is specified on CRITERIA.
GEMSCAL Generalized Euclidean metric individual differences model. The number of
directions for this model is set with the DIRECTIONS option on CRITERIA.
The number of directions specified can be equal to but cannot exceed the
group space dimensionality. By default, the number of directions equals the
number of dimensions in the solution.
Example
ALSCAL VARIABLES = V1 TO V6
/SHAPE = ASYMMETRIC
/CONDITION = ROW
/MODEL = GEMSCAL
/CRITERIA = DIM(4) DIRECTIONS(4).
• In this example, the number of directions in the GEMSCAL model is set to 4.
CRITERIA Subcommand
Use CRITERIA to control features of the scaling model and to set convergence criteria for the
solution. You can specify one or more of the following:
CONVERGE(n) Stop iterations if the change in S-stress is less than n. S-stress is a
goodness-of-fit index. By default, n=0.001. To increase the precision
of a solution, specify a smaller value, for example, 0.0001. To obtain
a less precise solution (perhaps to reduce computing time), specify a
larger value, for example, 0.05. Negative values are not allowed. If
n=0, the algorithm will iterate 30 times unless a value is specified with
the ITER option.
ITER(n) Set the maximum number of iterations to n. The default value is 30. A
higher value will give a more precise solution but will take longer to
compute.
STRESSMIN(n) Set the minimum stress value to n. By default, ALSCAL stops iterating
when the value of S-stress is 0.005 or less. STRESSMIN can be assigned
any value from 0 to 1.
NEGATIVE Allow negative weights in individual differences models. By default,
ALSCAL does not permit the weights to be negative. Weighted models
include INDSCAL, ASCAL, AINDS, and GEMSCAL. The NEGATIVE option
is ignored if the model is EUCLID.
CUTOFF(n) Set the cutoff value for treating distances as missing to n. By default,
ALSCAL treats all negative similarities (or dissimilarities) as missing,
and 0 and positive similarities as nonmissing (n=0). Changing the
CUTOFF value causes ALSCAL to treat similarities greater than or
equal to that value as nonmissing. User- and system-missing values
are considered missing regardless of the CUTOFF specification.