Ranges, Averages, and Variances in Software Productivity
The most common method for expressing data is to use average values, primarily the arithmetic mean. Although averages are interesting, they tend to be deceptive. This is because the ranges on either side of average values are quite broad for every software topic of interest:
image  Productivity
image  Schedules
image  Staffing
  Costs
  Defect potentials
  Defect removal efficiency levels
  Delivered defects ...

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