GEOG 892
Geospatial Applications of Unmanned Aerial Systems (UAS)

The Ever-confusing Statistical Terms

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The Ever-confusing Statistical Terms

To illustrate the different statistical terms we usually run into when we discuss data accuracy, let us consider the five error values (3-in., 2-in, 1-in., 5-in., and 4-in.) that were calculated on a population of data.

  1. Mean (average) = 3+2+1+5+4 5 =3.0
  2. Range = the distance between the largest error and the smallest error, i.e. Smallest = 1, Largest = 5 3)
  3. Variance = measure of spread or dispersion around the mean. It is the mean square of all the errors =( ( 33 ) 2 + ( 23 ) 2 + ( 13 ) 2 + ( 53 ) 2 + ( 43 ) 2 ) 1 51 = 0+1+4+4+1 4 = 10 4 =2.5 inc h 2
    Here, inch2 is a meaningless unit and a better statistical term to use is the standard deviation.
  4. Standard deviation, also called one-sigma, is the square root of the variance = = 2.5=1.581 inch ( is sample mean )
  5. Root Mean Square Error (RMSE)
    • RMSE is not Standard deviation or sigma; they are different.
    • Root Mean Square Error (RMSE) is computed as follows:
      RMSE =  ( Σ (  Z   Z i ) 2 / n )
      Where,
      Z = Measured Value from the data
      Zi = Control Value (field surveyed)
      n = number of measurements