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 <[email protected]> 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 > >
