15) In a recent clinical trial of three mechanical heart valves, one valve (Edwards-Duromedics) was used on even operation days; one valve (Bjork-Shiley) was used on odd operation days when the patient's year of birth was an even one; the third valve (Medtronic-Hall) was used on odd operation days when the patient's year of birth was an odd one. a. (5) Did this study employ an appropriate method to assign treatments? Comment on "allocation concealment". b. (5) What is the desired allocation ratio for this study based on the above description? c. (5) Describe how you would use simple randomization to generate treatment assignments for this study to obtain the desired allocation r