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SPSS® 12.0 Command Syntax Reference

SPSS® 12.0 Command Syntax Reference

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TWOSTEP CLUSTER 1593<br />

the first stage of clustering and values are added to its leaves if they are close to the cluster<br />

center of a particular leaf.<br />

Distance Measure. Two types of distance measures are offered—the traditional Euclidean distance<br />

and the likelihood distance. The former is available when no categorical variables are<br />

specified. The latter is especially useful when categorical variables are used. The likelihood<br />

function is computed using the normal density for continuous variables and the multinomial<br />

probability mass function for categorical variables. All variables are treated as independent.<br />

Tuning the Algorithm. You can control the values of algorithm-tuning parameters with the<br />

CRITERIA subcommand.<br />

Noise Handling. The clustering algorithm can optionally retain any outliers that do not fit in the<br />

CF tree. If possible, these values will be placed in the CF tree after it is completed. Otherwise,<br />

TWOSTEP CLUSTER will discard them after preclustering.<br />

Missing Values. TWOSTEP CLUSTER will delete listwise any records with missing fields.<br />

Numclusters. This subcommand specifies the number of clusters into which the data will be<br />

partitioned. The user may tell TWOSTEP CLUSTER to automatically select the number of<br />

clusters.<br />

Optional Output. You can specify output to an XML file with the OUTFILE subcommand. The<br />

cluster membership for each case used can be saved to the working data file with the SAVE<br />

subcommand.<br />

Weights. TWOSTEP CLUSTER ignores specification on the WEIGHT command.<br />

Basic Specification<br />

• The minimum specification is a list of variables, either categorical or continuous, to be<br />

clustered.<br />

• The number of clusters may be specified with the NUMCLUSTERS subcommand.<br />

• Unless the NOSTANDARDIZE subcommand is given, TWOSTEP CLUSTER will standardize<br />

all continuous variables.<br />

• If DISTANCE is Euclidean, TWOSTEP CLUSTER will accept only continuous variables.<br />

Subcommand Order<br />

• The subcommands can be specified in any order.<br />

<strong>Syntax</strong> Rules<br />

• Minimum syntax: a variable must be specified.<br />

• Empty subcommands are silently ignored.<br />

• Variables listed in the CONTINUOUS subcommand must be numeric.<br />

• If a subcommand is issued more than once, TWOSTEP CLUSTER will ignore all but the<br />

last issue.

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