Contents - Index

Tab 1: Histogram



Tab 1 of the Test Distribution window displays a histogram of the data along with the density of the selected distribution.  In the graphic above, the Pearson distribution was selected.  The parameters in parenthesis are the parameters of the distribution (average, standard deviation, skewness and kurtosis).   The normal distribution is shown if no distribution was selected or fit to the data.  Also shown are:

Moments:  The sample size, average, standard deviation, skewness and kurtosis (or excess kurtosis) of the data.

Test of Fit:  Two normality tests are performed.  When no transformation is selected, these tests are applied directly to data values and test for normality.  When a transformation/distribution is selected, these tests are applied to the transformed values and test for whether the selected distribution fits.  The first test is a general test for all departures from normality.  The Skewness-Kurtosis All test  (SK All) is the default test but the Anderson-Darling test (AD) and Shapiro-Wilks test (SW) are also available.  They can be selected using the Analysis Options dialog box or the popup menu described below.  The p-value and decision are given.  The test passes if the p-value > 0.05.  The second test is the Skewness-Kurtosis Specific test (SK Spec).  This test is designed to only reject for those departures from normality that invalid the tolerance interval and the confidence statement relative to the spec limits.  Passing this test indicates the statements are valid.  Only the Pass/Fail decision is given.  If the normality test fails, one can state: "With 95% confidence the data is not from the normal distribution."  If it passes, one can state: "No significant departure from normality was detected."

Capability Indexes:  Pp, Ppk and the estimated defect rate are shown.  The estimated defect rate may be in terms of percent in spec, percent out of spec or reliability, depending on the option selected in the Analysis Options dialog box and/or the Tolerance Interval Options dialog box.  The estimated defect rate assumes the selected distribution fits the data.  By default, it is only shown if the selected distribution fits the data.  This can be altered using the Analysis Options dialog box and/or the Tolerance Interval Options dialog box.  When a transformation/distribution is selected, the capability indexes and defect rate are calculated using the transformed values and spec limits.

Tolerance Interval and Confidence Statement Associated With Spec Limits:  These two statements assume the selected distribution fits the data.  By default, they are only shown if the selected distribution fits the data.  This can be altered along with the confidence level, etc. using the Analysis Options dialog box and/or the Tolerance Interval Options dialog box.  If the general test for normality passes, the statements are accurate.  If the general test fails but the Skewness-Kurtosis Specific test passes, the statements provide conservative bounds.  When a transformation/distribution is selected, these statements are calculated using the transformed values and spec limits.  The normal tolerance interval is then transformed back to the original units.

By performing a right mouse click over the graphic or clicking the Menu button, the following popup menu will appear:



The menu items are as follows:

Tolerance Interval Options ...:  Displays the Tolerance Interval Options dialog box for altering the confidence level, percentage in interval, type (upper, lower, 2-sided), units to use (% in spec, % out of spec, reliability) and whether to display tolerance interval only it the distribution fits.

Display Excess Kurtosis:  If checked, the excess kurtosis is display.  Otherwise the kurtosis is displayed..

Increase Number Cells in Histogram:  Selecting this menu item increases the number of cells in the histogram meaning fewer values fall in each cell.  This menu item can be selected multiple times.  This menu item is grayed out (not available) when the histogram is such that every unique value is contained in its own cell.

Decrease Number Cells in Histogram:  Selecting this menu item decreases the number of cells in the histogram meaning more values fall in each cell.  This menu item can be selected multiple times.

Use Anderson-Darling Test:  Selects Anderson-Darling test (AD) as general test for normality.

Use Shapiro-Wilks Test:  Selects Shapiro-Wilks test (SW) as general test for normality.

Use Skewness-Kurtosis All Test:  Selects Skewness-Kurtosis All test (SK All) as general test for normality.

Size To Fit:  Sizes plot to fit window.  Plot will shrink and expand to fit window when window is resized.

Fixed Size - Normal:  Sizes plot so easy to read.  If the plot is too large to fit the window, scroll bars are added.

Fixed Size - Custom:  Can specify the size of the plot.  If the plot is too large to fit the window, scroll bars are added.

Print:  Prints the plot.

Copy to Clipboard:  Copies the plot to the clipboard in Windows Meta file (Picture) format.

Copy Transformation Equation to Clipboard:  Copies the equation for the transformation to the clipboard in EXCEL format.