4PL model

Note a minimum of 5 dose points is required to fit a 4PL model.

and

where y is the response and x is the log (dose), for the reference standard and the test sample respectively.

is proportional to the slope at the midpoint.

> 0:

is the left asymptote

is the right asymptote

< 0:

is the right asymptote

is the left asymptote

is the log (dose) corresponding to the midpoint between

and

ε is an error term with distribution N(0,1) so σ_i ε is the error with distribution N(0, σ_i²), for i = Ref or Test.

QuBAS allows the user to select the ‘orientation’ of the model by choosing whether the left asymptote should be A or D. The four possible situations are:

A Left upper A left lower A right upper A right lower

For the parallel fit,

and the variance, σ², is common to all dose groups.

and

The contents of 4PL model

Analysis options

System Suitability Criteria

Sample Suitability Criteria

Relative potency