R help - Nov 2016 - drm function in drc package for fitting dose response curve

Hi all,
  When using drm function in drc package, we can fit several does response
curves simultaneously or fitting each curve separately. If we fit
simultaneous curves without any constraining condition, for example,
parallelism condition, will we get the same results as the results obtained
by fitting separate curves, particularly parameter estimates?
    If the results are different, what is the root differences, underlying
model and so on?
    Thanks much.
       Hanna

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