Methods and formulas for Poisson data in Analysis of Means

Use a Poisson distribution to represent data where the attribute of interest can appear an infinite number of times. Data include k counts. Listed below are the steps Minitab uses to compute ANOM results for data with a Poisson distribution.

  1. Computes the overall average of counts:
    • c̅ = Σk i=1 ci / k
  2. Compute an estimate of the standard deviation of the counts:
    • s = Sqrt (c̅)
  3. Determine the decision lines at significance α:
    • UDL = c̅ + hα s * Sqrt((k - 1)/ k)
    • LDL = c̅ - hα s * Sqrt((k - 1)/ k)

    where hα = inverse cumulative probability of α2 for the standard normal distribution, where α2 = 1 -α / (2 * k).

    If the number of rows in your response column (k) equal 2, then α2 = 1 -α / 2

  4. Plots the counts with the decision lines and the center line.
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