Some optimal matrix designs in stability studies

As part of an application for licensure of a new drug, it is necessary to provide data on the stability of the product over time under various conditions. If every combination of conditions is studied at every sampling time, the cost of the study can be substantial. To minimize expense, matrix designs are discussed, whereby only a fraction of the various design combinations of interest are tested at any specified sampling time. A method for choosing the time vectors such that the design is optimal in terms of maximum information per unit cost is proposed.