Sequential assignment and treatment-as-usual. Alternatives to standard experimental designs in field studies of treatment efficacy.

Psychosocial treatment research studies encounter obstacles to random assignment (RA). Used together, two procedures offer an alternative to the standard RA design. First, sequential assignment (SA) may create less opposition from administration, staff, and clients. SA operates on the principle that limited bed availability, a common treatment consideration in the field, determines assignment of clients to conditions. Second, treatment-as-usual (TAU) represents an alternative type of control condition. Some clients on the waiting list will, before a slot opens up and they enter an experimental condition, be absorbed into the existing treatment system, in which the amount and type of treatment they receive can vary widely. Substituting SA and TAU for the standard RA design may introduce methodological impurities including certain limited biases.