DELTA Subcommand (WLS command)

DELTA, alias POWER, is used in conjunction with the SOURCE subcommand to compute weights. DELTA specifies the values to use in computing weights. The weights are equal to 1/(SOURCE raised to the DELTA power).

  • The specification on DELTA is a list of possible delta values and/or value grids.
  • Multiple values and grids can be specified on one DELTA subcommand.
  • Delta values can be any value in the range of –6.5 to +7.5. Values below this range are assigned the minimum (–6.5), and values above are assigned the maximum (7.5).
  • A grid is specified by naming the starting value, the keyword TO, an ending value, the keyword BY, and an increment value. Alternatively, the keyword BY and the increment value can be specified after the starting value.
  • More than one DELTA subcommand can be specified; each subcommand will be executed.
  • If DELTA is not specified, the delta value defaults to 1.0.

Example

WLS VARIABLES = X1 WITH Y1 Z1
  /SOURCE=Z1
  /DELTA=0.5.
  • In this example, weights are calculated using the source variable Z1 and a delta value of 0.5. Thus, the weights are 1/(SQRT (Z1)).

Example

WLS VARIABLES = SHARES WITH PRICE
  /DELTA=0.5 TO 2.5 BY 0.5.
  • In this example, several regression equations will be fit, one for each value of delta.
  • Weights are calculated using the source variable PRICE (the default).
  • The delta values start at 0.5 and go up to 2.5, incrementing by 0.5. This specification is equivalent to 0.5 BY 0.5 TO 2.5.
  • The weights that maximize the log-likelihood function will be saved as variable WGT#1.