Denote by K n the convex hull of n independent random points distributed uniformly in a convex body K in R d , by V n the volume of K n , by D n the volume of K \K n , and by N n the number of vertices of K n . A well-known identity due to Efron relates the expected volume ED n -and thus EV n -to the expected number EN n+1 . This identity is extended from expected values to higher moments.The planar case of the arising identity for the variances provides in a simple way the corrected version of a central limit theorem for D n by Cabo and Groeneboom (K being a convex polygon) and an improvement of a central limit theorem for D n by Hsing (K being a circular disk). Estimates of varD n (K being a two-dimensional smooth convex body) and varN n (K being a d-dimensional smooth convex body, d ≥ 4) are obtained.The identity for moments of arbitrary order shows that the distribution of N n determines EV n−1 , EV 2 n−2 , . . . , EV n−d−1 d+1 . Reversely it is proved that these n −d −1 moments determine the distribution of N n entirely. The resulting formula for the probability that N n = k (k = d + 1, . . . , n) appears to be new for k ≥ d + 2 and yields an answer to a question raised by Baryshnikov. For k = d + 1 the formula reduces to an identity which has been repeatedly pointed out.