Using Histograms

This topic discusses how to use Histograms.

Page Name

Definition Name

Usage

Histogram Panel

None

Display the distribution analysis.

Histogram Options

None

Select options to modify the settings and display characteristics for histograms.

Mean Test

None

Run a means test against the histogram.

Standard Deviation Tests

None

Run a standard deviation test against the histogram.

Use the Histogram panel to display the distribution analysis.

Navigation:

  • Click the Histogram button.

  • Select View > Histogram.

This example illustrates the fields and controls on the Histogram pane. You can find definitions for the fields and controls later on this page.

 Histogram pane

The histogram display comprises multiple panes (sections) that display information about a subset. To resize a section:

  1. Place the cursor on the thick bar between the sections.

  2. Drag the edge of the section to the new size.

Click a cell and it becomes crosshatched to highlight it. When you click the Redraw button, the histogram is redrawn with the crosshatched cells removed. This is useful to examine a smaller portion of the data. By deleting cells, you can temporarily exclude the data values associated with that cell and recalculate the histogram and statistics.

To select a cell, drag the cursor across the vertical bar. The cell is highlighted in yellow. You can see the details of the selected cell in the detail section of the histogram.

Note: Cell values excluded from the graph are local to the active window; the dataset is not altered.

Title Section

This section displays the subset being analyzed for example, TEMP A.

Field or Control

Description

Observations

Displays the number of points used for the analysis.

Pearson Best-Fit, Tested for Normality, and Normality Assumed

Displays how the data distribution was assessed.

Chart Section

The section of the histogram displays the main body of the graph, with the following conditions:

  • (Optional) Specifications and +/- 3 sigma regions appear as dashed lines.

  • A thin, red, vertical line indicates the mean point.

  • The histogram is scaled by frequency on the left and by percent on the right.

  • (Optional) The distribution curve (indicated by a thick, red, curved line) overlays the chart.

List Section

This section displays summary statistics. You can change the statistics by changing graph preference settings. The statistics are calculated based upon the active data values for this subset.

Detail Section

This section is blank, unless you select a vertical bar (cell), in which case it displays detailed cell information. To select a cell, drag the cursor over the vertical bar, and it is highlighted in yellow.

Field or Control

Description

Cell # (cell number)

Displays the order of the individual cell in the histogram. For example, Cell #6 is the sixth cell in the sequence of cells displayed.

Width

Displays the dimension of the cell in the display.

Tally

Displays the total number of individual values in a cell.

% (percent)

Displays the percent of individual values in a cell.

Use the Histogram Options dialog box to select options to modify the settings and display characteristics for histograms.

Navigation:

Open a histogram.

Select Modify Graph > Settings.

You can modify the histogram by resizing the sections to adjust the amount of display information in each section of the graph. You can choose whether to display the overlay curve, the overlay specifications, or to overlay a box plot. You can change the number of cells displayed and the upper and lower specification limits.

Note: Any changes you make to the histogram are in effect only for the active chart. If you open a second histogram window, the changes are not in effect.

Field or Control

Description

Overlay Distribution Curve

Select to display a red bell curve line to overlay histogram cells.

Overlay Specs (overlay specifications)

Select to display blue, dashed, vertical lines for the upper specification limit (USL) and the lower specification limit (LSL).

Overlay Box and Whisker Plot

Select to display a box plot with the curve graph on the histogram.

Number of Cells

Indicate the number of cells displayed by the histogram. Move the slider or enter the number of cells in the settings box to the right to indicate how many cells you want between 4 and 30.

Note: The sample values are reordered to fit within the number of cells specified.

Spec Limits (specification limits)

Enter the limits in the Upper and Lower fields.

Use the Mean Test dialog box to run a means test against the histogram.

Navigation:

Open a histogram.

Select Tests > Mean Test.

Use mean tests to test the mean of the current sample versus a target mean and a confidence level.

To test for a mean:

  1. Enter the target mean and confidence level, or use the defaults.

  2. Click the Calculate button to see the results of the t Test calculation.

  3. Click the Done button to update the graph on the histogram.

Use the Stdev Test (standard deviation test) dialog box to run a standard deviation test against the histogram.

Navigation:

Open a histogram.

Select Tests > Stdev Test.

Use standard deviation tests to test the standard deviation of the current sample versus a target standard deviation and a confidence level.

To test for standard deviation:

  1. Enter the target standard deviation, or use the default.

    The standard deviation test has a limitation of df = 100. The sample size is display-only.

  2. Select a confidence level.

    Valid levels include:

    • 0.995

    • 0.990

    • 0.975

    • 0.950

    • 0.050

    • 0.025

    • 0.010

    • 0.005

  3. Click the Calculate button to see the results of the chi-squared test calculation.

  4. Click the Done button to update the graph on the histogram.