Patients in an outpatient treatment center receiving daily dressing changes were studied by means of ...

Patients in an outpatient treatment center receiving daily dressing changes were studied by means of a quasi-experimental design using a crossover strategy.
 
  Patients were administered either Morphine Contin or Percocet, by random assignment, on one day, and the other medication on the following day. Pain scores were obtained for both days, recorded and analyzed. Why was a crossover strategy used? (Select all that apply.)
  a. Because dressing changes may become less painful in some patients over time, as wounds heal, this strategy balanced the pain scores, across participants.
  b. Because dressing changes may become more painful over time, as debridement occurs, exposing raw tissue, this strategy balanced the pain scores, across participants.
  c. Because patients were not consented for the study and had to receive at least one traditional treatment.
  d. Because dressing changes may become less painful over time, as patients know what to expect, this strategy compensated by alternating first-treatment across patients.