The patient then waited through an extended period for healing. Then, in a surgery similar to those done to create vaginas for intersexed patients, surgeons constructed the patient's vagina by using skin grafts taken from her thighs or buttocks (Christine's vaginoplasty surgery was in 1954).
Experiments can be done in the field or in a laboratory. They can involve human or animal subjects. What distinguishes the type of experiment is the degree to which the experimenter can assign subjects to conditions. Three types are described here: True, Quasi- and Single-subject experiments. In a true experiment, subjects are randomly assigned to the treatment conditions (levels of the independent variable).
In quasi-experimental designs, outcomes may only be measured at the end of the study (rather than at the beginning and end), there may not be a control group, or patients may be assigned to the control and treatment groups by methods other than randomization.n 1979, in their classic textbook Quasi-Experimentation: Design and Analysis Issues for Field Settings Cook and Campbell describe quasi-experimental designs and their limitations. That work is the basis for the following discussion.