In the context of nonlinear regression models, a new class of optimum desig
n criteria is developed and illustrated. This new class, termed I-L-optimal
ity, is analogous to Kiefer's Phi(k)-criterion but is based on predicted va
riance, whereas Kiefer's class is based on the eigenvalues of the informati
on matrix; I-L-optimal designs are invariant with respect to different para
meterisations of the model and contain G- and D-optimality as special cases
. We provide a general equivalence theorem which is used to obtain and veri
fy I-L-optimal designs. The method is illustrated by various examples.