SPSS® 12.0 Command Syntax Reference

PROXIMITIES 1281
PH2 Phi-square between sets of frequencies. This is the CHISQ measure normalized
by the square root of the combined frequency. Therefore, its value
does not depend on the total frequencies of the two cases or variables
whose dissimilarity is computed.
Measures for Binary Data
CHISQ( xy , )
PH2( x, y)
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, PROXIMITIES 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. PROXIMITIES skips all other values.
• If only the first parameter is specified, PROXIMITIES uses that value to indicate presence
and all other values to indicate absence.
• If no parameters are specified, PROXIMITIES assumes that 1 indicates presence and 0
indicates absence.
Using the indicators for presence and absence within each item (case or variable), PROXIMITIES
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
=
=
Σi( xi – Ex ( i)
) 2
----------------------------------
( )
Σi( yi – Ey ( i)
) 2
+ ----------------------------------
( )
Ex i
PROXIMITIES 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 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
Ey i
Σi( xi – Ex ( i)
) 2
----------------------------------
Ex ( i)
Σi yi Ey ( – ( i)
) 2
+ ----------------------------------
Ey ( i)
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N