Statistical Measures

Ratios, Proportions, Rates

Proportions

• The second type of ratio, in which x is part of y, is also called a proportion (as in the previous "female/all" example).
• Proportions are usually expressed as percentages.

Examples of Ratios and Proportions

Independent x and y:
During the first 9 months of national surveillance for eosinophilia-myalgia syndrome (EMS), CDC received 1,068 case reports that specified sex; 893 cases were in females, 175 in males. Here is the method for calculating the female-to-male ratio for EMS.

1.	Define x and y:		x = cases in females
			y = cases in males
2.	Identify x and y:		x = 893
			y = 175
3.	Set up the ratio x/y:		893/175
4.	Reduce the fraction so that one value equals 1. Female to male = 893/175 = 5.1/1
5.	Express the ratio in one of the following ways: 5.1 to 1, or 5.1:1, or 5.1/1
Thus, there were just over 5 female EMS patients for each male EMS patient reported to CDC.