Surviving Andersonville

"Twenty-seven percent of the Union Army prisoners captured July 1863 or later died in captivity. At Andersonville the death rate may have been as high as 40 percent. How did men survive such horrific conditions? Using two independent data sets we find that friends had a statistically significant positive effect on survival probabilities and that the closer the ties between friends as measured by such identifiers as ethnicity, kinship, and the same hometown the bigger the impact of friends on survival probabilities"--National Bureau of Economic Research web site.