Statistics for Dummies Read Online Free PDF Page B

Crimes
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1987
13,508,700
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1988
13,923,100
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1989
14,251,400
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1990
14,475,600
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1991
14,872,900
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1992
14,438,200
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1993
14,144,800
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1994
13,989,500
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1995
13,862,700
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1996
13,493,900
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1997
13,175,100

    Is crime going up or down? It appears to be moving down in general, but you could look at these data in different ways and present these numbers in ways that make the trend look different. The big question is, do these data tell the whole story?
    For example, compare 1987 to 1993. In 1987 an estimated 13,508,700 crimes took place in the United States, and in 1993, the total number of crimes was 14,144,800. It looks like crime went up during those six years. Imagine if you were a candidate making a challenge for the presidency; you could build a platform around this apparent increase in crime. And if you fast-forward to 1996, the total number of crimes in that year was estimated to be 13,493,900, which is only slightly less than the total number of crimes in 1987. So, was very much done to help curb crime during the nine-year period from 1987 to 1993? In addition, these numbers don't tell the whole story. Is the total number of crimes for a given year the most appropriate statistic to measure the extent of crime in the United States?
    Another piece of important information has been left out of the story (and believe me, this happens more often than you may think)! Something else besides the number of crimes went up between 1987 and 1993: the population of the United States. The total population of the country should also play a role in the crime statistics, because when the number of people living in the country increases, you'd also expect the number of potential criminals and potential crime victims to increase. So, to put crime into perspective, you must account for the total number of people as well as the number of crimes. How is this done? The FBI reports a crime index, which is simply a crime rate. A rate is a ratio; it's the number of people or events that you're interested in, divided by the total number in the entire group.
    The lowdown on ratios, rates, and percents
    Statistics have a variety of different units in which they are expressed, and this variety can be confusing.
A ratio is a fraction that divides two quantities. For example, "The ratio of girls to boys is 3 to 2" means that for every 3 girls, you find 2 boys. It doesn't mean that only 3 girls and 2 guys are in the group; ratios are expressed in lowest terms (simplified as small as possible). So you could have 300 girls and 200 guys; the ratio would still be 3 to 2.
A rate is a ratio that reflects some quantity per a certain unit. For example, your car goes 60 miles per hour, or a neighborhood burglary rate is 3 burglaries per 1,000 homes.
A percentage is a number between 0 and 100 that reflects a proportion of the whole. For example, a shirt is 10% off, or 35% of the population is in favor of a four-day work week. To convert from a percent to a decimal, divide by 100 or move the decimal over two places to the left. To remember this more easily, just remember that 100% is equal to 1, or 1.00, and to get from 100 to 1 you divide by 100 or move the decimal over 2 places to the left. (And just do the opposite to change from a decimal to a percent.)
    Percentages can be used to determine how much a value increases or decreases, relatively speaking. Suppose the crimes in one city went up from 50 to 60, while the number of crimes in another city went up from 500 to 510. Both cities had an increase of 10 crimes, but for the first city, this difference is much larger, as a percentage of the total number of crimes. To find the percentage increase, take the "after" amount, minus the "before" amount and divide that result by the "before" amount. For the first city, this means crime went up by (60 – 50) ÷ 50 = 10 ÷ 50 = 0.20 or 20%. For the second city, this change reflects only a 2% increase, because (510 − 500) ÷ 500 = 10 ÷