Weibull Analysis: Results (Grouped Data) - Quick Tab

Use the options in this group box to change and/or display the parameters for the Weibull distribution. By default, the values in the Shape parameter and Scale parameter boxes will show the weighted least squares parameter estimates for the current data for the two-parameter Weibull distribution unless the parameter estimation procedure failed to converge (see the Introductory Overview).

Enter a value in this box (or use the accompanying microscrolls) to change the offset (threshold/location) parameter for the Weibull distribution.

Enter a value in this box (or use the accompanying microscrolls) to change the shape parameter for the Weibull distribution. This box is only available if the User-defined parameters option button is selected via the Estimate parameters (weighted least squares) group box on the

Estimate

tab.

Enter a value in this box (or use the accompanying microscrolls) to change the scale parameter for the Weibull distribution. This box is only available if the User-defined parameters option button is selected in the Estimate parameters (weighted least squares) group box on the

Estimate

tab.

Click this button to produce a spreadsheet with the current parameter values. If the current parameter values are the maximum likelihood weighted least squares parameter estimates (as estimated by selecting the ML shape & scale parameters option button - see

Estimate

tab), the spreadsheet will also contain the standard errors and confidence intervals for the parameter estimates. Note that the confidence intervals are adjusted to reflect the fact that the valid parameter space is bounded (i.e., the shape parameter must be greater than 0). See Nelson (1990; Section 5.7) or Dodson (1994) for computational details.

The percentiles for the confidence limits for the parameter estimates (see above) depend on the value entered into the CL (Confidence limit) box. By default, Statistica will compute 95% confidence intervals.

Click this button in order for Statistica to "read" the current value of the Offset (threshold/location) parameter, and then compute maximum likelihood parameter estimates for the Shape and Scale parameters based on the respective Offset (threshold/location) parameter. Note that this button is only available when you select the ML shape & scale params option button on the Weibull Analysis: Results (Grouped Data) - Estimate tab.