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Objectives Distinguish among rates, frequencies, proportions, and ratios; Construct crude and specific rates and differentiate these from adjusted rates; Discuss the need for and differentiate methods of standardization of rates; Differentiate between measures of frequency and measures of impact; Describe the interrelationship between incidence and prevalence; Calculate and interpret basic epidemiological measures to quantify health outcomes in the population; Identify common indicators used to…

### Ratio

It is obtained by dividing one quantity (numerator) by another (denominator) without implying any specific relationship between the numerator and the denominator.

If there are 5 apples and 10 oranges, it is expressed as follows:

5 : 10 or 5 / 10

### Proportion

It is a type of ratio. It describes outcome as a reflection of a part to the whole. It is typically expressed as percentages. For example, if there are 225 people in a room and 89 of these are males, males is 89 / 225 = 0.396. Multiply the answer by 100 to get the percentage: 0.396 x 100 = 39.6%.