Fragmentation functions and their role in determining the polarized   parton densities
  We extract the pion fragmentation functions and their uncertainties from a judicious choice of e+e- and semi-inclusive DIS data. These are used to study the error propagation in the extraction of polarized parton densities from semi-inclusive DIS asymmetries. We conclude that the uncertainties on polarized PDs have been underestimated in the past. 
S. Kretzer, E. Leader, E. Christova