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).
The third type of experiment is the observational experiment, which is used when there is no way to control variables. These types of experiments happen outside of the laboratory and may be called a non-experimental method. Just like the quasi-experimental type of method, there is a great deal of effort made to identify all variables that may be influential on the variable of interest.