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 = Σ^k _i=1 c_i / 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 + h_α s * Sqrt((k - 1)/ k)
   • LDL = c̅ - h_α s * Sqrt((k - 1)/ k)

   where h_α = 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.