The single most important determinant of camp survival was the number of men in POW camps. If everyone had been in a camp holding 7,500 men, survival probabilities would have been less than 60 percent instead of more than 80 percent. With greater camp populations survival probabilities would have been even lower. Another important determinant of camp survival was age. Had all men been of Thomas Withington’s age (47), only 70 percent of them would have survived. The next most important determinants of camp survivial were the number of friends, rank, and height. Men who were not either commissioned or noncommissioned officers fared poorly, as did those with no friends and those of Hnery Haven’s height.
Of course that is from the Civil War and it is from the new book by Dora Costa and Matthew Kahn. Here is my previous post about the book, see also the links suggested by Matt in the comments. You can buy the book here.