PASS

The Poisson probability law gives the probability distribution of the number of events occurring in a specified interval of time or space. The Poisson distribution is often used to fit count data, such as the number of defects on an item, the number of accidents at an intersection during a year, the number of calls to a call center during an hour, or the number of meteors seen in the evening sky during an hour.

The Poisson distribution is characterized by a single parameter which is the mean number of occurrences during the specified interval.

This procedure calculates the power or sample size for testing whether the ratio of two Poisson means is different from a specified value (usually one). The test procedure is described in Gu et al. (2008).

Minimum System Requirements
Click on one of the links below to view the minimum system requirements for NCSS and PASS products:
NCSS 8
PASS 11
PASS 2008
NCSS 2007
Previous Versions

Accuracy
We at NCSS have put a great deal of effort into finding the most accurate algorithms possible. The programs have been tested and verified over and over, both by us and by our customers. Each routine has been verified against textbooks, journal articles, and, where possible, other software. NCSS and PASS are some of the most accurate statistical analysis programs available. NCSS and PASS calculate with seventeen-digit, double-precision accuracy.

Guarantee
If you are not completely satisfied with an NCSS product during the first 30 days for any reason, return the program for a full, prompt refund (excluding shipping).