The rates at which a user can generate device-independent quantum random
numbers from a Bell-type experiment depend on the measurements that he
performs. By numerically optimising over these measurements, we present lower
bounds on the randomness generation rates for a family of two-qubit states
composed from a mixture of partially entangled states and the completely mixed
state. We also report on the randomness generation rates from a tomographic
measurement. Interestingly in this case, the randomness generation rates are
not monotonic functions of entanglement