One of the possible uncertainties in the extraction of the cross section asymmetries
(
,
) is in the estimation of the photon depolarization 
, which
includes the cross section ratio 
.
Post-EMC experiments uses the phenomenological formulae found in
Ref. [15], which is the arithmetic mean of the three different fits
to the data.
The threshold energy transfer is defined by 
and
the function
given by:
The EMC utilizes the formula
In Figure 4 all three expressions and EMC expression
are plotted with the data points measured at SLAC.
The uncertainty in
R is significant especially in the low-x region.
We can not choose one of three fits 
, 
, and 
according to current knowledge on 
.
That is why most of the experiments utilizes just
arithmetic mean of the three expressions.
It is, however, clear that 
underestimate
R in most region, and should be revised, although the
correction to depolarization 
is not very large.
Figure 4: Structure function 
is plotted
as functions of 
for several x-points.
Data points are from Ref.[15].
