Randomized trials of complex , non-pharmacologic interventions implemented in home and community settings , such as the University of Southern California ( USC ) - Rancho Los Amigos National Rehabilitation Center ( RLANRC ) Pressure Ulcer Prevention Study ( PUPS ) , present unique challenges with respect to ( 1 ) participant recruitment and retention , ( 2 ) intervention delivery and fidelity , ( 3 ) randomization and assessment , and ( 4 ) potential inadvertent treatment effects .