  In quantum optics the $g^{(2)}$-function is a standard tool to investigate
photon emission statistics. We define a $g^{(2)}$-function for electronic
transport and use it to investigate the bunching and anti-bunching of electron
currents. Importantly, we show that super-Poissonian electron statistics do not
necessarily imply electron bunching, and that sub-Poissonian statistics do not
imply anti-bunching. We discuss the information contained in $g^{(2)}(\tau)$
for several typical examples of transport through nano-structures such as
few-level quantum dots.
