Section 2.4

Fundamentals of Social Statistics by Adam J. McKee

Percentages & Rates

The term percent means per one hundred.  You can think of a percentage as a special fraction that always has 100 in the denominator.  For example, if males make up 49% of the population, then 49 out of every 100 people will be male.  Any fraction can be converted to a percentage.  This is very useful because it facilitates comparisons of things that would otherwise be hard to compare because they have different frequencies.

For example, a criminologist wanting to compare homicides in rural areas versus urban areas would not be able to use the actual number of homicides because there are far fewer people in rural areas, so homicides would be far more infrequent in those rural areas.  By using percentages (or rates), the criminologist has a better method of comparing Monticello, Arkansas (population 10,000) with New York City.

Computing a Percentage

To compute a percentage, simply divide the part by the whole and multiply the result by 100.  

For example, if 7 out of 113 convicted house burglars report carrying a firearm while committing their crime, the 6.2% reported carrying firearms in the commission of burglaries (7/113 = .062 x 100 = 6.2%).

A proportion is a part of one.  We compute a proportion following the same procedure we use to compute a percent, but we do not multiply the decimal number by 100.  That is, a proportion is a fractional part of a whole where the whole is always equal to one.  For example, a proportion of .50 is the same as saying 50% or the fraction ½.  Proportions are rarely ever reported in the popular press because the average person without the benefit of statistical training does not understand them.  Percentages are preferred.  Social scientists reporting research results in professional journals are far more likely to report findings as proportions.

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Last Modified:  06/03/2021

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