  We prove that the sizes of the maximal dissociated subsets of a given finite
subset of an abelian group differ by a logarithmic factor at most. On the other
hand, we show that the set $\{0,1\}^n\seq\Z^n$ possesses a dissociated subset
of size $\Ome(n\log n)$; since the standard basis of $\Z^n$ is a maximal
dissociated subset of $\{0,1\}^n$ of size $n$, the result just mentioned is
essentially sharp.
