Skip common site navigation and headers
United States Environmental Protection Agency
Exposure Research
Begin Hierarchical Links EPA Home > Research & Development > Exposure Research > Publications/Presentations > End Hierarchical Links

 

Proucl Version 3.0

spacer
spacer
Abstract:The computation ofa (l-a) 100% upper confidence limit (UCL) of the population mean depends upon the data distribution. Typically, environmental data are positively skewed, and a default lognormal distribution (EPA, 1992) is often used to model such data distributions. The H-statistic based Land's (Land 1971, 1975) H-UCL of the mean is used in these applications.

Hardin and Gilbert (1993), Singh, Singh, and Engelhardt (1997,1999), Schultz and Griffin,1999, Singh et al. (2002a), and Singh, Singh, and Iaci (2002b) pointed out several problems associated with the use of the lognormal distribution and the H-UCL of the population AM. In practice, for lognormal data sets with high standard deviation (sd), a, of the naturallog-transformed data (e.g., 0" exceeding 2.0), the H-UCL can become unacceptably large, exceeding the 95% and 99% data quantiles, and even the maximum observed concentration, by orders of magnitude (Singh, Singh, and Engelhardt, 1997). This is especially true for skewed data sets of smaller sizes (e.g., n < 50).

The H-UCL is also very sensitive to a few low or high values. For example, the addition of a sample with below detection limit measurement can cause the H-UCL to increase by a large amount (Singh, Singh, and Iaci, 2002b). Realizing that use of the H-statistic can result in unreasonably large UCL, it is recommended (EPA, 1992) to use the maximum observed value as an estimate of the UCL (EPC term) in cases where the H-UCL exceeds the maximum observed value. Recently, Singh, Singh and Iaci (2002b), and Singh and Singh (2003) studied the computation of the UCLs based upon a gamma distribution and several non-parametric bootstrap methods. Those methods have also been incorporated in ProUCL Version 3.0. ProUCL Version 3.0 contains fifteen UCL computation methods; five are parametric and ten are non-parametric. The non-parametric methods do not depend upon any of the data distributions.
spacer
Citation:Singh, A., R. Maichie, and A. K. Singh. Proucl Version 3.0. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-04/079, 2004.
spacer
spacer
Contact: Chris Siebert - (702) 798-2234 or siebert.christopher@epa.gov
spacer
Division: Environmental Sciences Division
spacer
Branch: Characterization & Monitoring Branch
spacer
Product Type: Pub Report
spacer
Published: 04/15/2004
spacer
Downloads:
spacer
Bullet Item Proucl Version 3.0
spacer
spacer
Related Entries:
spacer
Bullet Item Superfund Technical Support
spacer Relationship Reason:   A Project of the Product
spacer
spacer
spacer

 

ORD Home | Search EPA | Search NERL | Search EIMS | Contacts | Help

 
Begin Site Footer

EPA Home | Privacy and Security Notice | Contact Us

Last Updated on Monday, October 22, 2007
URL: http://cfpub.epa.gov