SPSS® 12.0 Command Syntax Reference

Measures for Binary Data
CLUSTER 231
Different binary measures emphasize different aspects of the relationship between sets of
binary values. However, all the measures are specified in the same way. Each measure has
two optional integer-valued parameters, p (present) and np (not present).
• If both parameters are specified, CLUSTER uses the value of the first as an indicator that
a characteristic is present and the value of the second as an indicator that a characteristic
is absent. CLUSTER skips all other values.
• If only the first parameter is specified, CLUSTER uses that value to indicate presence and
all other values to indicate absence.
• If no parameters are specified, CLUSTER assumes that 1 indicates presence and 0 indicates
absence.
Using the indicators for presence and absence within each item (case or variable), CLUSTER constructs
a 2 ×
2 contingency table for each pair of items in turn. It uses this table to compute a
proximity measure for the pair.
Item 2 characteristics
Present Absent
Item 1 characteristics
Present a b
Absent c d
CLUSTER computes all binary measures from the values of a, b, c, and d. These values are
tallied across variables (when the items are cases) or across cases (when the items are
variables). For example, if variables V, W, X, Y, Z have values 0, 1, 1, 0, 1 for case 1 and values
0, 1, 1, 0, 0 for case 2 (where 1 indicates presence and 0 indicates absence), the contingency
table is as follows:
Case 2 characteristics
Present Absent
Case 1 characteristics
Present 2 1
Absent 0 2
The contingency table indicates that both cases are present for two variables (W and X), both
cases are absent for two variables (V and Y), and case 1 is present and case 2 is absent for one
variable (Z). There are no variables for which case 1 is absent and case 2 is present.
The available binary measures include matching coefficients, conditional probabilities,
predictability measures, and others.
Matching Coefficients. Table 1 shows a classification scheme for matching coefficients. In
this scheme, matches are joint presences (value a in the contingency table) or joint absences
(value d). Nonmatches are equal in number to value b plus value c. Matches and nonmatches
may be weighted equally or not. The three coefficients JACCARD, DICE, and SS2 are related
monotonically, as are SM, SS1, and RT. All coefficients in Table 1 are similarity measures,