Graphs and Charts
Box Graph
The box symbol summarizes the distribution of data within a data set. A box symbol consists of a rectangle and lines that extend from both ends (whiskers). The ends of the rectangle designate the 25th and 75th percentiles of the data set. The ends of the whiskers designate the 10th and 90th percentiles. The line across the rectangle indicates the median value (the 50th percentile).
Based on this information, a User can make observations about key values (median, 75th percentile etc.) and whether the data is symmetrical, tightly grouped or skewed.
Box Graph Trend
The Box Graph Trend displays the data trend for all stored versions of the same Specification. The trend graph makes it easy to compare key values and see if the data have improved or not.
Scatter Graph
The Scatter Graph is a two-dimensional plot of individual data. The Vertical axis displays the Quality value for a requirement, while the horizontal axis displays the Information value. The scale goes from 0% to 100% for both Information and Quality. A good plot would be to have values in the upper right corner of the Scatter graph, while a bad plot would be to have most values in the lower left corner.
Trend-line Graph
The Trend-line Graph is used to display metrics that indicate size, such as the number of serious issues. The graph draws diamonds for the moving average, while the non-stifled line is a regression line for the moving average. Note that the moving average value found in the graph is not identical to the value found in the General metrics table. The stifled lines indicate a 3-σ value of the moving average trend. Individual values that lie outside the 3-σ boundaries can indicate that the process is not stable.
u Chart
A u Chart is used mostly for rates, such as the number of serious issues per requirement. When the number of requirements change between different versions of a Specification, u Charts are better to use than XmR charts.
The u Chart displays diamonds for individual data. The Centre Line is depicted by CL in the graph, while the Upper and Lower Control Limits are depicted by UCL and LCL in the graph. Individual data points that lie above the UCL boundary or below the LCL boundary can indicate that the process is not stable.
XmR Chart
Individuals and Moving Range (XmR) charts are mostly used for metrics that are independent of Specification size, such as readability indicators.
The graph contains two charts: one for individual data and one for the Moving Range data. Both charts contain a Centre Line (CL). The Individual chart contains an Upper Control Limit (UCL) and a Lower Control Limit (LCL), while the Moving Range chart contains an UCL only.
More Information
For more information on process stability, see "Measuring the Software Process, Statistical Process Control for Software Process Improvement, by William A. Florac and Anita D. Carleton, Addison-Wesley 1999, ISBN 0-201-60444-2".