Semi-Nonquantitative ???

Rob Jordan jordan at mbcrr.harvard.edu
Thu Feb 9 09:40:47 EST 1995


In article <1995Feb6.181928.13508 at govonca.gov.on.ca>,
kruschb at govonca.gov.on.ca (Brian Kruschel) wrote:


> 
> I (being an analytical chemist for many years) regard semi-quantitative
> results to mean that the numbers are rough, as in an order of magnitude. 
> For example, I analyze some well-water for benzene and in a
> semi-quantitative report I would say that there was approximately 5 parts
> per million benzene.  I could dilute and re-run this sample many times and
> get the analysis down to 4,578 parts per billion, but 5 ppm is
> semi-quantitative.  Also the instruments available now will analyze down
> to low ppb or low micrograms per cubic liter or meter (whichever the
> matrix), so when we get gross amounts (ie ppm levels) we prefer not to
> waste the time doing 6 or 7 dilutions to get an exact number.
> 
 Brian,

Your description of semi-quantitative was very satisfying. In essence you
are saying that semi-quantitative indicates a certain amount of error in
your measurement but that for the conclusion you are trying to make with
semi-quantitative data this amount of error is OK. Moreover, the term
semi-quantitative suggests that there are more accurate ways of making the
same measurement. 

I still don't like the term. I would rather see the data and a statement
of the amount of error in the measurement. In biology I have often found
that people use the term semi-quantitative when they don't have
appropriate controls in their experiments, yet they still try to make
quantitative interpretations of the data. I think biolgists often misuse
this term. 

Thanks again,

Rob J.

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