Abstract
In this paper, we develop testing procedures for hypotheses regarding the difference of location parameters from two independent two-parameter exponential populations with unknown but proportional scale parameters. We design appropriate two-stage and purely sequential procedures to determine the appropriate sample sizes while controlling both type-I and type-II error probabilities at or below the preassigned levels α, β respectively. We prove that both two-stage and purely sequential testing strategies enjoy a number of practically appealing properties. Extensive sets of computer simulations validate our theoretical findings. We illustrate the testing methodologies along with sampling procedures on a cancer studies data.