Figure 6. Correspondence of classifier score and biological differentiation criterion.
Per cell we measured the longest neurites 
and diameters 
on day 
(blue) and 
(red) without (circles) and with mitomycin (triangles) of cells receiving NGF stimulation. Transparent points represent individual cell and neurite length measurements per image and bold symbols depict the respective mean values (with 
% c.i.) of the classifier score (
) of image 
and the quantity 
on the given day. If this value is larger than 
, marked by the vertical dotted line, the length of the longest neurite of a cell is at least 
times the cell diameter. This is a commonly used biological threshold criterion for differentiation. The correlation with the respective FDA scores is 
and the fitted linear regression line (black line, 
% c.i. shown in grey) has a positive slope of 
. Therefore, the neurite length to cell diameter ratio is proportional to the classifier score. The threshold of 
of the biological criterion corresponds to a threshold of 
of the classifier on average (horizontal dotted line), i.e. choosing this threshold for the FDA will result in a decision of the FDA which is (on average) equivalent to the biological definition.