Adding Fitted Normal Curves to a Comparative Histogram

COMPHISTOGRAM Statement

Adding Fitted Normal Curves to a Comparative Histogram

See CAPCMH1 in the SAS/QC Sample Library

In Figure 3.2, it appears that each lot produces transistors with channel lengths that are normally distributed. The following statements use the NORMAL option to fit a normal distribution to the data for each lot (the observations corresponding to a specific level of the classification variable are referred to as a cell). The normal parameters $\mu$ and $\sigma$ are estimated from the data for each lot, and the curves are superimposed on each component histogram.

   proc capability data=channel noprint;
      specs lsl = 0.8  clsl = black  llsl = 2
            usl = 2.0  cusl = black  lusl = 3 ;
      comphist length / class      = lot
                        nrows      = 3
                        intertile  = 1
                        cprop      = green
                        normal(color = yellow)
                        cframe     = ligr
                        cfill      = blue
                        cframeside = ligr;
      label lot = 'Transistor Source';
   run;

The comparative histogram is displayed in Figure 3.3.

Figure 3.3: Fitting Normal Curves

Specifying INTERTILE=1 inserts a space of one percent screen unit between the framed areas, which are referred to as tiles. The shaded bars, added with the CPROP= option, represent the relative frequency of observations in each cell. See "Dictionary of Options" for details concerning these options.

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