Dennis R Helsel
Affiliation: U.S. Geological Survey
- Fabricating data: how substituting values for nondetects can ruin results, and what can be done about itDennis R Helsel
U S Geological Survey, P O Box 25046, MS 964, Lakewood, CO 80225, USA
Chemosphere 65:2434-9. 2006..Substituting values for nondetects should be used rarely, and should generally be considered unacceptable in scientific research. There are better ways...
- Regional Kendall test for trendDennis R Helsel
U S Geological Survey, P O Box 25046, MS 964, Lakewood, Colorado 80225, USA
Environ Sci Technol 40:4066-73. 2006..Yet often also of interest is whether a consistent trend is evident throughout the entire region. This paper adapts the Seasonal Kendall trend test to determine whether a consistent regional trend occurs in environmental variables...
- Complications with using ratios for environmental data: comparing enantiomeric ratios (ERs) and enantiomer fractions (EFs)Elin M Ulrich
U S Geological Survey, National Water Quality Laboratory, Denver, CO 80225, USA
Chemosphere 53:531-8. 2003..The use of nonparametric statistical summaries, e.g., median and percentiles, provides a more robust indicator of the typical value and spread for both ER and EF data...
- More than obvious: better methods for interpreting nondetect dataDennis R Helsel
U S Geological Survey, Lakewood, CO, USA
Environ Sci Technol 39:419A-423A. 2005
- Methyl tert-butyl ether (MTBE) in public and private wells in New Hampshire: occurrence, factors, and possible implicationsJoseph D Ayotte
U S Geological Survey, NH VT Water Science Center, 361 Commerce Way, Pembroke, New Hampshire 03275, USA
Environ Sci Technol 42:677-84. 2008..From 2003 to 2005, MTBE occurrence decreased in 63 public-supply wells and increased in 60 private-supply wells, but neither trend was statistically significant...