Are the Statistics Deceptive?

1. Are the Statistics Deceptive? CSIT 58 Chapter 11

2. Unknowable and Biased Statistics • Statistics are evidence expressed as numbers. • Often just educated guesses or estimates because of difficulties in collecting data • Lack of truthfulness • Failure to report events • Physical barriers to observing events

3. Clues for Assessing Statistics • How were the statistics obtained? • What type of calculation was used? • Do the statistics prove the conclusion or something else? • Compare the necessary statistical evidence with what is actually provided. • Form your own conclusion from the statistics and ask “Is there missing information?”

4. Confusing Averages There are three different ways to determine an average: Mean: Add all of the values and divide the total by the number of values Median: List all of the values from highest to lowest and find the one in the middle Mode: Find the value that appears most frequently

5. An Average is an Average? These are the number of downloads of popup ad window blocker programs from Download.com. See what a difference there is in the averages?

6. Conclude This, Prove That Pay close attention to the wording of the statistics and the wording of the conclusion to see whether they are referring to the same thing. The financial problems of our public schools are highly overrated. In 1992-93, an average $6,100 was spent on every public school student in the United States. Furthermore, full-time public school teachers make an average $34,027 per year according to the American Federation of Teachers. This salary is not at all bad, compared to the 1990 median income of $34,400 of families in the U. S.. It isn’t insufficient funding or ill-paid teachers that are killing the educational system; it is, instead, the lack of well-trained teachers thanks to grossly lax colleges of education.

7. Conclude This, Prove That The conclusion is: The educational system is being killed by the lack of well-trained teachers thanks to grossly lax colleges of education. Reasons: Average $6,100 spent on each student 1992-1993 Teachers make average $34,027 (median of 1990 was $34,400) • Is anything proven about the quality of teacher training? • What kind of average is $6,100? • A median is not a great way to compare salaries and why was 1990 used instead of 1992-93?

8. Missing Information What further information do you need before you can judge the impact of the statistics? Our new police chief John Neu is not doing his job. The fact is that Torrance is becoming a more dangerous place to live. According to the latest statistics, the number of crimes went from 1,471 to 1,537. That’s a 4.5% increase. During the same time period, other South Bay cities became safer. Manhattan Beach had 47 less crimes than the year before and Hawthorne had 86 fewer crimes.

9. What’s Missing? This argument that the Torrance police chief isn’t doing his job is based on statistics about the crime rate. You might want to know: • What was the pattern for crime in previous years in Torrance? Maybe the current year was unusual for some reason. • How many total crimes were there in Manhattan Beach and Hawthorne? • How did other local cities compare? • What kind of crimes increased? Was it homicide, rape, assault or auto theft?

10. More Information • Torrance had extremely low crime numbers in 2004 and 2004. • Manhattan Beach went from 356 in 2005 to 309 in 2006 (-13%). Hawthorne went from 2,406 to 2,320 (-3.6%). • Crime in Rancho Palos Verdes increased by 13%. Rolling Hills increased by 75%. Lawndale decreased by 2.7%. Lomita was unchanged. • There was a spike in the number of aggravated assaults in Torrance in 2006. Burglary and auto theft rose a little. Rape and robbery decreased. Source: Altman, Larry. “South Bay Crime Report.” Daily Breeze. Sun. 11 March 2007. Page A1.

11. As Compared to….? Another form of missing information is the lack of relevant comparisons. Americans belief in the value of international education was not shaken after the Sept. 11 terrorist attacks. A recent poll (March 2002) showed that 77% of the public supported international course requirements in college. More information about the poll at: http://www.acenet.edu/programs/international/mapping/intl_summary2.cfm

12. The Relevant Comparison How does 77% support compare to previous years? It was actually the same as the April 2000 survey. Among other things, you might also be curious about: • Who was “the public” surveyed? Did they have college-age children? • How were the survey questions worded? Would so many have been favorable if the students were going to the middle east to study? • Who is ACE? Do they have a reason to push international education?

13. What’s Wrong with the Statistics? Marriage drives men to drink and the problem seems to be getting worse. Married men are twice as likely as bachelors to become alcoholics, as evidenced by the fact that 66% of all male alcoholics are married. In addition, the problem has increased over the past 10 years, suggesting that marriage is becoming increasingly stressful to the average male. Statistics collected by the state of Michigan show that there were over 15,000 married male alcoholics in 1998, compared with only 12,000 in 1988. (From Asking the Right Questions 6th Ed. p. 172)

14. The Relevant Comparison • Concludes that marriage causes men to become alcoholic. All you can really conclude is that more (two thirds) of alcoholics are married. • How were people categorized as alcoholic? By asking them straight out? • The statistics are misleading. Need to know: • The percentage of married men who are alcoholic versus the percentage of single men who are. • The percentage of men who were alcoholics in 1998 vs. 1988. There could be more men. End of lecture