  A number of recent experiments report the low-temperature thermopower
$\alpha$ and specific heat coefficients $\gamma=C_V/T$ of strongly correlated
electron systems. Describing the charge and heat transport in a thermoelectric
by transport equations, and assuming that the charge current and the heat
current densities are proportional to the number density of the charge
carriers, we obtain a simple mean-field relationship between $\alpha$ and the
entropy density $\cal S$ of the charge carriers. We discuss corrections to this
mean-field formula and use results obtained for the periodic Anderson and the
Falicov-Kimball models to explain the concentration (chemical pressure) and
temperature dependence of $\alpha/\gamma T$ in EuCu$_2$(Ge$_{1-x}$Si$_x$)$_2$,
CePt$_{1-x}$Ni$_x$, and YbIn$_{1-x}$Ag${_x}$Cu$_4$ intermetallic compounds. %
We also show, using the 'poor man's mapping' which approximates the periodic
Anderson lattice by the single impurity Anderson model, that the seemingly
complicated behavior of $\alpha(T)$ can be explained in simple terms and that
the temperature dependence of $\alpha(T)$ at each doping level is consistent
with the magnetic character of 4{\it f} ions.
