  In magnetic resonance, the bulk magnetization of a sample that is being
measured is typically defined as a quantity proportional to spin polarization.
The fact that all spins of the same type contribute equally to measurable
signals is considered obvious. By focusing on nuclear spin ensembles, we prove
the high-field theorem for a general case of spin-I: grouping of spins in
molecules does not affect the total measurable NMR signal given thermal
equilibrium at high field ($\hbar \gamma B_0 \gg |H_{int}|$, where $|H_{int}|$
is the characteristic amplitude of internal spin-spin interactions). We
demonstrate this first by analyzing equations for spin magnetization and then
for a general case using the density matrix formalism. We exemplify the theorem
implications by predicting NMR signal intensities for ensembles of molecules
containing single, two, and three spins. The theorem is not applied in more
intricate situations, such as zero- to ultralow-field conditions and far from
thermodynamic equilibrium. Considering the populations of rotation levels, the
thermal equilibrium polarization at HF and low temperature for H2 gas
illustrate one of the intricate cases.
