  We consider the statistical relationship between the growth rate of activity
in the early phase of a solar cycle with its subsequent amplitude on the basis
of four datasets of global activity indices (Wolf sunspot number, group sunspot
number, sunspot area, and 10.7-cm radio flux). In all cases, a significant
correlation is found: stronger cycles tend to rise faster. Owing to the
overlapping of sunspot cycles, this correlation leads to an amplitude-dependent
shift of the solar minimum epoch. We show that this effect explains the
correlations underlying various so-called precursor methods for the prediction
of solar cycle amplitudes and also affects the prediction tool of Dikpati et
al. (2006) based upon a dynamo model. Inferences as to the nature of the solar
dynamo mechanism resulting from predictive schemes which (directly or
indirectly) use the timing of solar minima should therefore be treated with
caution.
