Extracting information measures from limited experimental samples, suc
h as those normally available when using data recorded in vivo from ma
mmalian cortical neurons, is known to be plagued by a systematic error
, which tends to bias the estimate upward. We calculate here the avera
ge of the bias, under certain conditions, as an asymptotic expansion i
n the inverse of the size of the data sample. The result agrees with n
umerical simulations, and is applicable, as an additive correction ter
m, to measurements obtained under such conditions. Moreover, we discus
s the implications for measurements obtained through other usual proce
dures.