Introduction: Control Chart XmR
The most effective way to detect signals of change in your KPI is to use a Control Chart
The Control Chart helps you to determine if your processes are in control. When your measurements meet certain criteria (see below), an indicator immediately tells you something is going on. This helps you to determine the source of this variation.
The Control Chart XmR consists of two charts: The upper chart (X-Chart) displays the data points over time together with a calculated average. The calculated average is then used to calculate the Upper and Lower Control Limits (UCL and LCL). The lower chart displays the Moving Range (mR-Chart) with its Average and Upper Control Limit. The mR-Chart can be hidden.
The rule set for the detection of signals is customisable. By default it is:
- A point is outside the control limits;
- 7 points in a row are above or below the center line;
- 10 out of 12 points are above or below the center line;
- 3 out of 4 points are closer to the UCL or LCL than the center line.
Besides these rules (known as the Wheeler Rules) you can also apply the Nelson Rules. These detect signals in the following situations:
- One point is more than 3 standard deviations from the mean;
- Nine (or more) points in a row are on the same side of the mean;
- Six (or more) points in a row are continually increasing (or decreasing);
- Fourteen (or more) points in a row alternate in direction, increasing then decreasing;
- Two (or three) out of three points in a row are more than 2 standard deviations from the mean in the same direction;
- Four (or five) out of five points in a row are more than 1 standard deviation from the mean in the same direction;
- Fifteen points in a row are all within 1 standard deviation of the mean on either side of the mean;
- Eight points in a row exist, but none within 1 standard deviation of the mean, and the points are in both directions from the mean.
You can add your own target line(s), to see how your process is doing compared to a certain goal. If you have determined the center line and control limits separately, you can easily add these to the visual as well.
Key features of the Control Chart XmR are:
- Switch between standard and trending XmR: processes with natural trends (continuously increasing or decreasing) can be analysed with the Trending XmR function;
- Highlight signals: detected signals can be indicated below the chart, and the measurements themselves can be coloured in a separate colour;
- Work on various time scales: choose the appropriate time scale for optimal analysis, ranging from seconds to years;
- Format objects: all lines, markers and axes can be formatted independently, and support theme settings;
- Selection & Highlighting: like in standard Power BI Charts you can make use of the Selection & Highlighting functions within the Control Chart XmR;
- Context menu: like in standard Power BI Charts you have access to the context menu to include and exclude data points;
- Full Tooltip support: besides the default Tooltip behaviour (show the value of the element you hover) you can also add additional fields to the tooltip;
- Full Bookmark support: like any of the standard visuals the Control Chart XmR supports Bookmarks.
How to use: Build visual
To use the Control Chart XmR, you need to have a dataset with at least a date-field and a numeric field. The available fields are:
- Axis: here you add the category you want to use as your x-axis. Make sure to use the actual dates instead of the Date Hierarchy.
- Actuals: this field contains your measurements.
- Target: this field contains your target points, which can be shown as a line or a sequence of markers. Multiple targets are supported, you can add up to three categories.
- Central line: the Central Line will be calculated automatically. You can add your own Central Line by including it in this field.
- Control limits: the Control Limits (or natural process limits) are calculated automatically, but can be added here. You can add two categories to this bucket: one for the lower limit and one for the upper limit. The order doesn’t matter.
- Signals: an indicator will be shown in the chart as soon as this field is non-empty. You can have an indicator for every point in your Date field.
- Tooltips: the fields added here will show up in the tooltip when the user hovers a specific data point.
How to use: Format visual
The Control Chart XmR comes with many of the standard Power BI formatting options. Titles, axis labels, line and markers appearance, etc.: it’s all there.
- License: here you can enter your license information to disable any license reminders.
- Legend: here you can switch off/on the legend, enable and add your own Title and set the Color and Text Size.
- X-axis: by default the Axis type is set to Continuous, in the Date type option you can define the formatting of the date labels on the X-axis. The options range from Years to Seconds. Note that making changes to this option does not invoke any changing to the grouping of your data. You can also set the Axis type to Categorical. You can also format the text and title, the available options are Color, Text size, Font family, Title color, Title text, Title text size, Title font and Title position.
- Y-axis: here you can set a Start/ End value and format the Color, Text size, Font family, Display Units and Decimal Places. Switch off/on the Title and format the Style, Title color, Title text, Title text size, Title font and Title Position or format the Line style, Color, Stroke width of the Gridlines.
- Data Colors: set here the colors for the Actual line, and (if enabled) the markers on that line. In the Actual (outside Control Limits), for highlighting purposes, you can change the color of the Actual markers when they fall outside the Control Limits bandwidth. The Actual line itself will not change color when outside the control limits. You can also change the color for the Target, Central line, Control limits and Signals.
- Data point: contains all options to format the lines and markers in both parts of the chart such as the Actual line width, the CL line width and the Marker size. You can enable the Show actual markers, Show target Line, Show 1 sigma and 2 sigma-lines options. Enable the Show CL as step when you want to show the Central Line stepped. By default the Show target markers and Show control limits area options are on.
- Show MR: toggle this option on to see the mR chart, displaying the moving Range.
- Calculation: by default the rules are set to Wheeler, here you can set to apply the Nelson Rules, switch on/off the options Recalculate on signals (available if the Central line field is empty), Trending XmR and Show signals or set the Data values for Average. By default the Rules are set to Wheeler and Recalculate is on. See below more information on the Calculation options.
- Zoomslider: enable the zoomslider option to easily examine a smaller range of the date in the Control XmR chart without having to use a filter. The zoomslider is added on the chart’s x-axis if the date-axis is enabled. Click and drag endpoints on sliders to adjust the dimensions of the chart, slide both endpoints toward the center. The closer the two endpoints are to each other, the more you zoom in to display shorter, finer segments. Click and hold down the left mouse button on the center section of the zoom bar and then scroll left or right to a particular point. You can also click on the label to display and select from the Calendar instead. You can also change the Font color, size and family of the zoomslider.
- Statistics per Rule: enable this option and then click in the visual either the Focus mode icon or the ellipsis called More options and select Show as a table to see a table with all statistics about the applied rules; you can switch off/ on the Show title option and change the Title font color, size and family. This table is particularly helpful if you would like to be able to know which rules are breaking on a recurring basis on your control charts.
The General settings contain options that affect the visual container and are consistent across all visual types. Here you can also customize the general Title and Tooltips.
Here you will find the options that affect your analysis the most. You can change the number of points considered for the average and each rule, and more:
- Auto recalculation: Turning this option on will induce a recalculation when Rule 2, 3 or 4 (if enabled) is violated. A new center line and control limits is calculated. When the option is turned off, then the center line will be based on the points as defined by the parameter Data values for Average.
- Trending XmR: Turn this option on if you have a measurement with a naturally increasing / decreasing behaviour. All rules remain the same, but the CL becomes a slope which best fits your data.
- Show signals: when one of the rules is violated, then a small indicator will be shown in the chart. In case you have add a field to the Signal bucket, then non-empty values will also result in an indicator. Hover over the indicator to see which rule has been violated.
- Data values for Average: This option determines how many points are used to calculate the center line and control limits. Make sure that this value is lower than the number of data points you have.
If Rules are set as Wheeler
- Rule 1: A point is outside the control limits (doesn’t invoke recalculations).
- Rule 2: n points in a row are above or below the center line. The n can be changed, default is 7.
- Rule 3: n out of n+2 points are above or below the center line. The n can be changed, default is 10.
- Rule 4: n out of n+1 points are closer to the UCL or LCL than the center line. The n can be changed, default is 3.
If Rules are set as Nelson
- Rule 1: One point is more than 3 standard.
- Rule 2: Nine (or more) points in a row are on the same side of the mean.
- Rule 3: Six (or more) points in a row are continually increasing (or decreasing).
- Rule 4: Fourteen (or more) points in a row alternate in direction, increasing then decreasing.
- Rule 5: Two (or three) out of three points in a row are more than 2 standard deviations from the mean in the same direction.
- Rule 6: Four (or five) out of five points in a row are more than 1 standard deviation from the mean in the same direction.
- Rule 7: Fifteen points in a row are all within 1 standard deviation of the mean on either side of the mean.
- Rule 8: Eight points in a row exist, but none within 1 standard deviation of the mean, and the points are in both directions from the mean.
For any questions or remarks about this Visual, please contact us by email at Nova Silva Support or visit the community forum.