Confederate Amnesty Records for the United States Civil War, 1863-1866 is based on oaths of surrendering soldiers.
“This data collection was designed to compare the heights of southern whites with those of slaves and northern white males between 1863 and 1866. Information provided includes month, day, and year of amnesty, county and state, age, color of skin, eyes, and hair, occupation, last name, first name, oath administrators, feet component in height, inch component in height, and height in inches.”
Comparable historical studies include:
and several more studies by Robert Fogel and others.