maximum permissible limits, was cancer incidence discussion

[Ruth Sponsler <jk5554@YAHOO.COM>]

To clarify: Actually, I was making a comment about

epidemiological studies (it related to the earlier

discussion of the NSWS) in response to another post. 

My comment had to do with studies that look for cancer

(or other diseases) in a population.  I was trying to

point out that some epidemiologists try to 'cheat' by

using one-sided confidence limits whereas the proper

method is to use a two-sided limit when evaluating

causes of mortality in a population.



The question about 'maximum permissible' exposure came

after my remark, and I am afraid I do not know the

answer to it, as I'm not an expert on the regulations.



~Ruth 2





--- Jerry Cohen <jjcohen@prodigy.net> wrote:

> Ruth,

>     I don't think your response really addresses

> Franz's query. The

> determination of whether "maximum permissible"

> exposures are exceeded

> would require only a one-sided (high end)

> evaluation. In determining whether

> a speed limit is exceeded, it is not necessary to

> test how slow the vehicle

> might have been going.

>     The problem in evaluating compliance with MPC

> criteria lies in the fact

> that exposure levels are not uniform and generally

> vary  stochastically

> (both spatially and temporally). Any single

> measurement gives only the

> ambient concentration for one given location and

> time period.

> A series of measurements will  show various results.

> Since exposure

> levels vary stochastically, there will always be

> some finite (non-zero)

> possibility

> that MPC levels might have been exceeded. Whether

> that possibility must be

> below the 1, 2, 3, 5 , 10 or whatever sigma level to

> be "acceptable" has not

> been addressed.

>     When exposure limits (MPC's,  TLV's, etc) were

> originally

> conceived, they were intended to provide guidance

> for the professional

> judgment of industrial hygienists, health

> physicists, and other health

> professionals. They were not intended to be rigid

> regulatory limits.

> Unfortunately, these guidelines were later codified

> into laws & regulations

> including penalties for exceeding these limits.

>     So, getting back to Franz's question, when

> should exposure limits be

> considered violated? When the probability that they

> might be exceeded is:

> 0.1, 0.01, 0.001, 0.000001,   or what? One may need

> to a lawyer, politician,

> or theologian to answer that.  I am sure that,

> provided sufficient funding,

> the NCRP would be happy to study the problem and let

> us know what further

> study might be needed to reach a solution.          

>                Jerry

> 

> 

> > >This reason is exactly why statistics profs

> advise

> > >people doing _research_ to use 2-sided confidence

> > >limits, and discourage the practice of 1-sided

> limits

> > >in most cases.  [1-sided limits have some valid

> > >applications in non-research fields such as

> quality

> > >control and business management].





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