SPSS® 12.0 Command Syntax Reference

PROBIT 1271
• This example reads four variables and requests a default analysis with an estimate of the
natural response rate.
• The predictor variable, DOSE, has a value of 0 for the third case.
• The response count (10) and the observation count (100) for this case establish the initial
estimate of the natural response rate.
• Because the default log transformation is performed, the control group is not included in
the analysis.
Example
DATA LIST FREE / SOLUTION DOSE NOBSN NRESP.
BEGIN DATA
1 5 100 20
1 10 80 30
1 0 100 10
...
END DATA.
PROBIT NRESP OF NOBSN BY SOLUTION(1,4) WITH DOSE
/NATRES = 0.10.
• This example reads four variables and requests an analysis in which the natural response
rate is set to 0.10. The values of the control group are ignored.
• The control group is excluded from the analysis because the default log transformation is
performed.
PRINT Subcommand
Use PRINT to control the statistics calculated by PROBIT.
• PROBIT always displays the plot (for a single-predictor model) and the parameter estimates
and covariances for the probit model.
• If PRINT is used, the requested statistics are calculated and displayed in addition to the
parameter estimates and plot.
• If PRINT is not specified or is specified without any keyword, FREQ, CI, and RMP are
calculated and displayed in addition to the parameter estimates and plot.
DEFAULT FREQ, CI, and RMP. This is the default if PRINT is not specified or is specified by
itself.
FREQ Frequencies. Display a table of observed and predicted frequencies with their
residual values. If observations are entered on a case-by-case basis, this listing can
be quite lengthy.
CI Fiducial confidence intervals. Print Finney’s (1971) fiducial confidence intervals
for the levels of the predictor needed to produce each proportion of responses.
PROBIT displays this default output for single-predictor models only. If a categorical
grouping variable is specified, PROBIT produces a table of confidence intervals
for each group. If the Pearson chi-square goodness-of-fit test is significant (p < 0.15
by default), PROBIT uses a heterogeneity factor to calculate the limits.