If you tell a friend that in 1860 there were 5616 slaves in Augusta County, your friend would probably reply, "Out of how many people?" By itself, the number 5616 is not very informative. It means one thing if there were only 6000 people in Augusta County. It means quite another if there were 27749, as reported by the 1860 U.S. Census. One way to make raw census data more meaningful is to express variables as a proportion or percentage of their total number.
Proportions, which take the form of fractions or decimal values, vary between 0 and 1. The formula to calculate a proportion is:
Percentages are more frequently used to analyze census data than proportions. Percentages can be obtained from proportions by simply multiplying by 100. Their value varies between 0 and 100. The formula to calculate a percentage is:
Applying this formula to our example: (5616 slaves/27749 total people)*100=20.2. Thus, we can say that slaves accounted for 20.2 percent of Augusta County's total population. This gives us a much better feel for the density of the slave population in Augusta County than our original figure of 5616 slaves. Because percentages standardize for population size (the word "per cent" actually means "per hundred"--we are calculating the number of slaves per hundred people) we can also use this figure to compare Augusta County with Virginia, or the South as a whole, when similar figures are computed for those regions.