Histogram Interval Midpoints and Endpoints

The CAPABILITY Procedure

Histogram Interval Midpoints and Endpoints

By default, histogram intervals are centered on the major tick marks of the horizontal axis. The major tick mark values are the midpoints of the histogram intervals. The midpoints are evenly spaced, and the difference between consecutive midpoints is used as the width of the histogram bars. The CAPABILITY procedure determines the number of intervals using the algorithm described in Terrell and Scott (1985).

You can specify the number of intervals and their midpoint values with the MIDPOINTS=value-list option in a HISTOGRAM or COMPHISTOGRAM statement. In a COMPHISTOGRAM statement, you can specify MIDPOINTS=KEY or MIDPOINTS=UNIFORM. If you specify MIDPOINTS=KEY, the procedure first determines the midpoints for the data in the key cell using the method of Terrell and Scott (1985). It then extends the midpoint list for the key cell in both directions as necessary until it spans the data in the remaining cells. If you specify MIDPOINTS=UNIFORM, the procedure determines the midpoints using all the observations as if there were no cells.

In a HISTOGRAM statement you can specify the number of histogram intervals using the NMIDPOINTS= option. The CAPABILITY procedure then determines the midpoint values.

You can specify the ENDPOINTS option in a HISTOGRAM statement to produce a histogram whose interval boundaries, or endpoints, are aligned with major tick marks on the horizontal axis. The procedure uses the method of Terrell and Scott (1985) to determine the number of histogram intervals. The number of major tick marks on the horizontal axis of the resulting histogram is the number of intervals plus one. The least major tick mark value is the lower bound of the first interval and the greatest value is the upper bound of the last interval.

You can use the ENDPOINTS=value-list option in a HISTOGRAM or COMPHISTOGRAM statement to specify the number of interval endpoints and their values. The number of values is one greater than the number of intervals on the resulting histogram. You can specify ENDPOINTS=KEY or ENDPOINTS=UNIFORM in a COMPHISTOGRAM statement. The number of intervals is determined just as with MIDPOINTS=KEY or MIDPOINTS=UNIFORM, but the interval boundary values will not be the same, in general.

You can use the NENDPOINTS= option in a HISTOGRAM statement to align interval endpoints with major tick marks and to specify the number of endpoints. The procedure determines the endpoint values. If you specify the ENDPOINTS= or NENDPOINTS= option, you need not specify the ENDPOINTS option.

The ENDPOINTS=, MIDPOINTS=, NENDPOINTS=, and NMIDPOINTS= options are mutually exclusive. The MIDPOINTS= option takes precedence over the NMIDPOINTS= option, and the ENDPOINTS= options takes precedence over the NENDPOINTS= option. The ENDPOINTS= and NENDPOINTS= options override either MIDPOINTS= or NMIDPOINTS=.

Chapter Contents
Previous
Next
Top