  Indications of a possible composition-dependent fifth force, based on a
reanalysis of the E\"{o}tv\"{o}s experiment, have not been supported by a
number of modern experiments. Here, we argue that searching for a
composition-dependent fifth force necessarily requires data from experiments in
which the acceleration differences of three or more independent pairs of test
samples of varying composition are determined. We suggest that a new round of
fifth-force experiments is called for, in each of which three or more different
pairs of samples are compared.
