U-charts and c-charts are used for Poisson data rather than binomial. U is for defects per unit and c for counts. While similar to the P or NP charts, the control limits are based on a Poisson distribution.

In this recipe, we will type data for falls and beds occupied per month at a hospital into the worksheet. We will then use the u-chart to plot the number of falls in a hospital per occupied bed. The results are displayed as a per-unit figure.

This data is loosely based on an example discussed in the paper, Plotting basic control charts: tutorial notes for healthcare practitioners, by M.A. Mohammed, P. Worthington, and W. H. Woodall.

This paper is available at the following location:

http://medqi.bsd.uchicago.edu/documents/ControlchartsmohammedQSHC4_08.pdf

The data is given with monthly results in separate columns for ease of data entry. We will first transpose the data before plotting it on a u-chart. As the minimum number of occupied beds is within 75 percent of the maximum...