Distribution Analyses |

After choosing **Curves:QQ Ref Line**, you can use the **QQ Ref Line** dialog to add distribution reference lines to QQ plots.

**Figure 38.35:** QQ Ref Line Dialog

The default adds a least squares regression line. You can also specify your own reference line by choosing **Method:Specification** and specifying both the intercept and slope.

If you select a **Weight** variable, you can add a weighted least squares regression line to the normal QQ plot. If the data are normally distributed with mean and standard deviation and if each observation has approximately the same weight (*w _{0}*), then the least squares regression line has approximately intercept and slope for vardef=WDF/WEIGHT and slope for vardef=DF/N.

A normal QQ plot with a least squares reference line is shown in Figure 38.36. Use the sliders to change the intercept and slope of the reference line.

**Figure 38.36:** Normal QQ Plot with a Reference Line

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