  Spin-dependent lepton-nucleon scattering data have been used to investigate
the validity of the concept of quark-hadron duality for the spin asymmetry
$A_1$. Longitudinally polarised positrons were scattered off a longitudinally
polarised hydrogen target for values of $Q^2$ between 1.2 and 12 GeV$^2$ and
values of $W^2$ between 1 and 4 GeV$^2$. The average double-spin asymmetry in
the nucleon resonance region is found to agree with that measured in
deep-inelastic scattering at the same values of the Bjorken scaling variable
$x$. This finding implies that the description of $A_1$ in terms of quark
degrees of freedom is valid also in the nucleon resonance region for values of
$Q^2$ above 1.6 GeV$^2$.
