[1] A person is selected to work as a fitting model primarily on criteria matching the desired measurement specifications of the designer or manufacturer.
[2] These specifications generally consist of height, bust-waist-hip circumference, arm and leg length, shoulder width, and a myriad other measurements as indicated by the garment type.
This is the case whether the garments are for women or men of any size; the grading of construction patterns is often tested on a variety of fitting models to be sure that increases in size are translated accurately and evenly across the range.
[4] The measurements and proportions vary based on size as well as age.
[1] Many major brands make clothes in juniors and missy sizes.