Tab 4: Plot - Variation
Tab 4 of the Analysis Results window displays a plot of the variation in time order. Also displayed are the control limits in red. The control limits are those for the standard deviation or CV. These control limits assume the values come from the normal distribution and may not be appropriate for all sets of data. The changes detected by the change-point analysis are indicated by changes in the background color. If individual values per time period are being analyzed, the standard deviations or CVs plotted are determined by calculating the differences between consecutive points. If there are multiple samples per time period, the standard deviations of CVs of each time period are plotted.
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:
Displays Changes in Background: Displays changes in the variation on Tab 5. Changes are represented by changes in the background color. Selecting this menu item hides the changes.
Use Median Standard Deviation: Uses the median of the subgroup standard deviations to estimate the within subgroup standard deviation used to calculate control limits on Tab 1 and on this tab. Also effects the estimate of the standard deviation on Tab 5. This is the default estimate. The median standard deviation is more robust to outliers.
Use Average Standard Deviation: Uses the average of the subgroup standard deviations to estimate the within subgroup standard deviation used to calculate control limits on Tab 1 and on this tab. Also effects the estimate of the standard deviation on Tab 5. The average standard deviation is more sensitive to outliers.
Display Control Limits: When checked, the control limits are displayed in red. Select this menu item to hide the control limits.
Connect Points: When checked, the points are connected by line segments. Select this menu item to hide the connecting line segments.
Show All Points in Window: Selecting this menu item causes the plot to maintain a ratio of length to width of 2.5. This makes it easy to view the entire plot. However, with large data sets, the points may be so closely spaced it is difficult to distinguish individual points. Setting this menu item automatically selects the Size to Fit menu item below.
Space Points so Each Visible: Selecting this menu item causes the ratio of length to width to be set so as to make all the points easily visible. This frequently causes the plot to get very long requiring that one scroll across the plot to view the entire plot. Selecting this menu item automatically selects the Fixed Size - Custom menu item below.
Plot Options...: Displays Plot Options dialog box for changing the style and captions of the plot. A short cut is to double click on the feature of the plot one wants to change. For example, double click on the title displays the Plot Option dialog box with the Title tab showing.
Save Style of Variation Plot: The style is set using the Plot Options menu item above. Selecting this menu item saves this style in the system registry. This allows this style to be quickly applied to other plots.
Set Variation Plot to Saved Style: The style is set using the Plot Options menu item and saved using the Save Style of Variation Plot menu item above. Selecting this menu item sets the plot to a previously saved style.
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.