[ RadSafe ] RE: Comparison of a Measured Resultto the Critical/Decision Level; new question

[roseb at gdls.com]

Dr. Harm:

On 10/05/2009, 07:23 AM, Dr Arvic Harms wrote:

>It is common to assign a value of [y# divided by factor of 2] to the 
'less than y#' results. Is there any scientific justification for doing 
this? 

I had the same question in 2007 regarding how to handle "censored" data. 
Below are articles that provide brief discussions of the bases for and 
limitations associated with the treatment of censored data, to include the 
LOD/2 method, for data that is less than the limit of detection (LOD):

1. Perkins, J. L., G. Cutter, M. Cleveland: Estimating the mean, variance, 
and confidence limits from censored (<limit of detection), 
lognormally-distributed exposure data.  Am. Ind. Hyg. Assoc. J. 51(8): 
416-419 (1990).  [Online] Available at 
http://www.informaworld.com/smpp/content~db=all~content=a727071549 
(October 5, 2009)

2. Succop, P. A., S. Clark, M. Chen, W. Galke: Imputation of data values 
that are less than a detection limit.  J. Occup. Environ. Hyg, 1(7): 
436?441 (2004).  [Online] Available at 
http://www.informaworld.com/smpp/content~db=all~content=a713774462 
(October 5, 2009)

3. Glass, D. C., C. Gray: Estimating mean exposures from censored data: 
exposure to benzene in the australian petroleum industry.  Ann. Occup. 
Hyg. 45(4): 275-282 (2001).  [Online] Available at 
http://annhyg.oxfordjournals.org/cgi/reprint/45/4/275 (October 5, 2009)

4. Stefaniak, A. B., et al: Summary of historical beryllium uses and 
airborne concentration levels at Los Alamos National Laboratory.  Appl. 
Occup. Environ. Hyg. 18(9): 708-715 (2003).  [Online] Available at 
http://oeh.informaworld.com/soeh/search October 5, 2009)

5. Barr, D. B., et al: A survey of laboratory and statistical issues 
related to farmworker exposure studies.  Environ. Health. Perspect. 
114(6): 961-968 (2006).  [Online] Available at 
http://www.ehponline.org/members/2006/8528/8528.pdf (October 5, 2009) (See 
discussion of "Statistical Issues at the
Analysis Stage," p. 964)

6. ?Analysis of ozone and fine particulate matter in the northeastern 
united states.?  Final report 03-05.  New York State Energy Research and 
Development Authority (NYSERDA).  November, 2003.  [Online] Available at 
http://www.nyserda.org/programs/Environment/EMEP/NYSERDAreport03-04.pdf 
(October 5, 2009)

National Institute for Occupational Safety and Health, Division of 
Physical Sciences and Engineering: Analyzing workplace exposures using 
direct reading instruments and video exposure monitoring techniques. 
Publication no. 92-104.  U.S. Department of Health and Human Services, 
Centers for Disease Control and Prevention. August, 1992.  [Online] 
Available at http://www.cdc.gov/niosh/92-104.html (October 5, 2009) (See 
discussion at VIII.C., pp 20-23)

I found the above articles useful withe respect to helping me understand 
the bases and limitations of methods for treating censored data to include 
LOD/2.

Henry Rose

Boyd H. Rose, CM, CIH, CHMM
Sr. Safety and Environmental Engineering Specialist
Corporate Radiation Safety Officer
General Dynamics Land Systems
38500 Mound Road
Mail Zone 436-10-75
Sterling Heights , MI 48310-3269
Tel: 586 825 4503
Fax: 586 825 4015
E-mail: roseb at gdls.com





This is an e-mail from General Dynamics Land Systems. It is for the intended recipient only and may contain confidential and privileged information.  No one else may read, print, store, copy, forward or act in reliance on it or its attachments.  If you are not the intended recipient, please return this message to the sender and delete the message and any attachments from your computer. Your cooperation is appreciated.