Ian,
thanks - I think I had it backwards after reading your first post and
thought of controllable errors being those that can be brought "under
conrtol" by sampling, whereas uncontrollable would be those that cannot
be sampled and therefore their amplitude is unknown.
Yet you also seem to agree that characterization is dependent on
specifics of experimental setup, leaving the door open for the
possibility that noise-vs-bias choice may be driven by experimental
circumstance.
And in practice, wouldn't it be more consistent to stick with the
definition that statistical error/noise/precision is defined by what is
really sampled? Because if some factor is not sampled, I have zero
knowledge of the corresponding error magnitude. I agree with Tim that
not sampling what can be easily sampled is a poorly designed experiment,
but it can also be characterized (which is probably a nicer term) as an
experiment with large systematic error (due to poor design).
Cheers,
Ed.
On Wed, 2013-03-13 at 12:33 +0000, Ian Tickle wrote:
> Ed, sorry for delay. I was not trying to make any significant
> distinction between "controllable" and "potentially controllable":
> from a statistical POV they are the same thing. The distinction is
> purely one of practicality, i.e. within the current experimental
> parameters is it possible to eliminate the systematic error, for
> example is there a calibration step where you determine the systematic
> error by use of a standard of known concentration. The error is still
> controllable regardless of whether you actually take the trouble to
> control it! Note that the experimental setup has not changed, you are
> merely using the same apparatus in a different way but any random
> errors associated with the measurements will still be present.
>
>
> Of course if you change the experimental setup (note that this
> potentially includes the experimenter!) then all bets are off! It's
> very important to describe the experimental setup precisely before you
> attempt to characterise the errors associated with a particular setup.
>
>
> BTW I agree completely with Kay's analysis of the problem: as he said
> "you are sampling (once!) a statistical error component". This is
> what I was trying to say, he just said it in a much more concise way!
> This random (uncontrollable) error then gets propagated through the
> sequence of steps in the experiment along with all the other
> uncontrollable errors.
>
> Cheers
>
>
> -- Ian
>
>
>
> On 11 March 2013 19:04, Ed Pozharski <[log in to unmask]> wrote:
> Ian,
>
> thanks for the quick suggestion.
>
> On Mon, 2013-03-11 at 18:34 +0000, Ian Tickle wrote:
> > Personally I tend to avoid the systematic vs random error
> distinction
> > and think instead in terms of controllable and
> uncontrollable errors:
> > systematic errors are potentially under your control (given
> a
> > particular experimental setup), whereas random errors
> aren't.
> >
>
> Should you make a distinction then between controllable
> (cycling cuvette
> in and out of the holder) and potentially controllable errors
> (dilution)? And the latter may then become controllable with
> a
> different experimental setup?
>
> Cheers,
>
> Ed.
>
> --
> I don't know why the sacrifice thing didn't work.
> Science behind it seemed so solid.
> Julian, King of Lemurs
>
>
>
--
Edwin Pozharski, PhD, Assistant Professor
University of Maryland, Baltimore
----------------------------------------------
When the Way is forgotten duty and justice appear;
Then knowledge and wisdom are born along with hypocrisy.
When harmonious relationships dissolve then respect and devotion arise;
When a nation falls to chaos then loyalty and patriotism are born.
------------------------------ / Lao Tse /
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