Bioequivalence and Bioavailability Forum

Dear ElMaestro!

❝ I will try to "reformulate" (that's a forbidden word otherwise!)

❝ The weighting scheme I encounter now and then is the 1/x or 1/x². Lets for the time being forget the 1/y or 1/y² (which deserves discussion in another thread).

Yes!

❝ […] the choice of weights has to do with variabilities […]

❝ Therefore, my intuition tells me that your equation is intended for a situation with no weights and where the variability is not constant.

Your intuition essentially told you the right thing. In bioanalytics variance is never constant. When weighing was not possible due to computational limitations (the famous TI-59 and HP-41 were top instruments then) analysts went for logarithmic spacing. To be honest I started with eye-ball regression by means of graph paper and a transparent ruler.
Even today people are disappointed that weighted regression is not available in M$-Excel.
Actually nobody goes with equidistant calibrators if more than one order of magnitude is covered, so it’s difficult to tell. Like you I would expect that logarithmic spacing would more often lead to a unweighted fit of proper ‘quality’ (based on back-calculations).