RT Journal Article SR Electronic T1 Environmental Monitoring: Data Trending Using a Frequency Model JF PDA Journal of Pharmaceutical Science and Technology JO PDA J Pharm Sci Technol FD Parenteral Drug Association (PDA) SP 254 OP 260 VO 58 IS 5 A1 Ross A. Caputo A1 Anne Huffman YR 2004 UL http://journal.pda.org/content/58/5/254.abstract AB Environmental monitoring programs for the oversight of classified environments have used traditional statistical control charts to monitor trends in microbial recovery for classified environments. These methodologies work well for environments that yield measurable microbial recoveries. However, today successful increased control of microbial content yields numerous instances where microbial recovery in a sample is generally zero. As a result, traditional control chart methods cannot be used appropriately. Two methods to monitor the performance of a classified environment where microbial recovery is zero are presented. Both methods use the frequency between non-zero microbial recovery as an event. Therefore, the frequency of events is monitored rather than the microbial recovery count. Both methods are shown to be appropriate for use in the described instances.