Skills to Develop
- Describe the range of applications of statistics
- Identify situations in which statistics can be misleading
- Define "Statistics"
Statistics include numerical facts and figures. For instance:
- The largest earthquake measured \(9.2\) on the Richter scale.
- Men are at least \(10\) times more likely than women to commit murder.
- One in every \(8\) South Africans is HIV positive.
- By the year \(2020\), there will be \(15\) people aged \(65\) and over for every new baby born.
The study of statistics involves math and relies upon calculations of numbers. But it also relies heavily on how the numbers are chosen and how the statistics are interpreted. For example, consider the following three scenarios and the interpretations based upon the presented statistics. You will find that the numbers may be right, but the interpretation may be wrong. Try to identify a major flaw with each interpretation before we describe it.
1) A new advertisement for Ben and Jerry's ice cream introduced in late May of last year resulted in a \(30\%\) increase in ice cream sales for the following three months. Thus, the advertisement was effective.
A major flaw is that ice cream consumption generally increases in the months of June, July, and August regardless of advertisements. This effect is called a history effect and leads people to interpret outcomes as the result of one variable when another variable (in this case, one having to do with the passage of time) is actually responsible.
2) The more churches in a city, the more crime there is. Thus, churches lead to crime.
A major flaw is that both increased churches and increased crime rates can be explained by larger populations. In bigger cities, there are both more churches and more crime. This problem, which we discuss in more detail in the section on Causation in Chapter 6, refers to the third-variable problem. Namely, a third variable can cause both situations; however, people erroneously believe that there is a causal relationship between the two primary variables rather than recognize that a third variable can cause both.
3) \(75\%\) more interracial marriages are occurring this year than \(25\) years ago. Thus, our society accepts interracial marriages.
A major flaw is that we don't have the information that we need. What is the rate at which marriages are occurring? Suppose only \(1\%\) of marriages \(25\) years ago were interracial and so now \(1.75\%\) of marriages are interracial (\(1.75\) is \(75\%\) higher than \(1\)). But this latter number is hardly evidence suggesting the acceptability of interracial marriages. In addition, the statistic provided does not rule out the possibility that the number of interracial marriages has seen dramatic fluctuations over the years and this year is not the highest. Again, there is simply not enough information to understand fully the impact of the statistics.
As a whole, these examples show that statistics are not only facts and figures; they are something more than that. In the broadest sense, "statistics" refers to a range of techniques and procedures for analyzing, interpreting, displaying, and making decisions based on data.
Online Statistics Education: A Multimedia Course of Study (http://onlinestatbook.com/). Project Leader: David M. Lane, Rice University.
- Mikki Hebl