Abstract
This column features “bits” of information sampled from a variety of sources that may be of interest to teachers of statistics. Bob abstracts information from the literature on teaching and learning statistics, while Bill summarizes articles from the news and other media that may be used with students to provoke discussions or serve as a basis for classroom activities or student projects. We realize that due to limitations in the literature we have access to and time to review, we may overlook some potential articles for this column, and therefore encourage you to send us your reviews and suggestions for abstracts.
From the Literature on Teaching and Learning Statistics
Computational Statistics and Statistical Education
ed. Ene-Margit Tiit (1997). Proceedings of the Tartu Conference, Tartu, Estonia, June 3–8, 1996.
The preface to the Proceedings states that “The collection of reports reproduced in the ‘Proceedings’ reflects a ‘statistically representative sample’ of the problems discussed at the conference. The first part of the book, ‘Statistical Software as an Environment for Teaching Statistics,’… contains the papers of these authors who have approached the problems from the viewpoint of computational statistics. The second part of the book, ‘Statistical Education ‐‐ Where Are We Going?’ carries the spirit expressed in the papers of the invited speaker Anne Hawkins and other specialists of statistical education.”
Contents:
Part One. Statistical Software as an Environment for Teaching Statistics
“Why Computational Statistics and Statistical Education” by Ene-Margit Tiit
“Making S-Plus an Environment for Communicating Ideas” by Peter Naeve
“Requirements for Software Tools to Better Support Students' Learning to Practise Flexible Data Analysis” by Rolf Biehler
“Teaching Statistics through Problem-Based Learning” by Peter Anton, Per Arnqvist, and Staffan Uvell
“Computer Aided Instruction to Statistical Decisions in Schools” by Tibor Nemetz and Zolton Hives
Part Two. Statistical Education ‐‐ Where Are We Going?
“Statistical Education ‐‐ Past, Present and Future” by Anne Hawkins
“Simple Experiments: A Structural Approach for Teaching Experimental Design” by June Juritz
“How Far Have We Come? Do We Know Where We Are Going?” by Anne Hawkins
To inquire about obtaining a copy of the proceedings, send an e-mail message to Carmen Batanero ([email protected]).
Multimedia and New Educational Environments: Statisticians and Experts Exchange Views
ed. Maria Gabriella Ottaviani (1996). A seminar organised under the auspices of Dipartimento di Statistica, Probabilita e Statistiche Applicate, Rome University “La Sapienza.”
This book presents articles by seven Italian authors on the use of multimedia, hypertext, and computer simulations in the teaching of statistics. Each article is printed in both Italian and English. The contents of the book are as follows:
“Introduction” by Maria Gabriella Ottaviani
“Multimedia Communication and Models of Learning Environments” by Luciano Galliani
“The Computer and Teaching Statistics” by Maria Gabriella Ottaviani
“Hypertexts and Teaching Statistics: Navigation Strategies” by Furio Camillo and Marco Pedroni
“Teaching Basic Statistics Following a Multimedia Approach” by Agostino Di Ciaccio
“A Multimedia Approach to Teaching Mathematics for Finance” by Silvana Stefani and Anna Torriero
“Multimedia Products for Statistics and Economics” by Simone Borra
“Multimedia and Teaching in a Statistics Research Bureau” by Silvio Stoppoloni
To inquire about obtaining a copy of the book, send an e-mail message to Maria Gabriella Ottaviani ([email protected]).
“Probability, Matrices, and Bugs in Trees”
by Paula Grafton Young (1998). The Mathematics Teacher, 91(5), 402–406, 412–415.
The article describes an interesting problem that can be addressed by probability modeling. The author states the problem as follows: “Suppose that three trees are located around a small lake or pond. One of the trees becomes infested with an insect population that destroys the leaves or fruit of the tree.” The article describes activities which use basic probability, simple random walks, matrices, and Markov chains to model the path of a single insect and to determine the spread of the insect population to the remaining trees. Example activity sheets are provided in appendices.
“Making the Grade – AP Statistics, 1997”
by Richard L. Schaeffer (1998). STATS: The Magazine for Students of Statistics, No. 22, 8–12.
The author provides a perspective on the Advanced Placement Statistics Exam by describing its history, the content and structure of the exam, grading schemes, results of a comparability study, and implications for student preparation.
“On the Job: A Day in the Life of a Statistician at Los Alamos National Laboratory”
by Jane Booker (1998). STATS: The Magazine for Students of Statistics, No. 22, 17–19.
Jane Booker is a group leader of the Statistics Group at Los Alamos National Laboratory. This article can provide students with a good idea of the work and challenges that statisticians encounter in their careers.
The American Statistician: Teacher's Corner
“Perspectives on Implementing Statistical Modeling and Design (SMD) in an Industrial/Chemical Environment”
by Karen D. Rappaport, Nouna Kettaneh, and Svante Wold (1998). The American Statistician, 52(2), 152–159.
In the competitive environment of today's chemical industry, an efficient approach of experimentation is necessary in all facets of research and development. This article discusses the tools of statistical modeling and design in this perspective, and reports the development of a program for the increased use of these tools at Hoechst Celanese Corporation, on international chemistry and polymers company based in New Jersey, USA.
“Student Projects on Statistical Literacy and the Media”
by Andrew Gelman and Deborah Nolan with Anna Men, Steve Warmerdam, and Michelle Bautista (1998). The American Statistician, 52(2), 160–166.
An important theme in an introductory statistics course is the connection between statistics and the outside world. This article describes some assignments that have been useful in getting students to learn how to gather and process information presented in the newspaper articles and scientific reports they read. We discuss two related assignments. For the first kind of assignment, students work through prepared instructional packets. Each packet contains a newspaper article that reports on a scientific study or statistical analysis, the original report on which the article was based, a worksheet with guidelines for summarizing the reported study, and a series of questions. In the second kind of assignment, each student is required to find a newspaper article themselves, track down the original report, summarize the study using our guidelines, and write a critique of the article. Here, we describe the guidelines we developed to help the student in reading the newspaper article and original source, and the procedures we used for each type of assignment. Examples of handouts and assignments appear as appendixes.
“Some Class-Participation Demonstrations for Decision Theory and Bayesian Statistics”
by Andrew Gelman (1998). The American Statistician, 52(2), 167–174.
We present several classroom demonstrations that have sparked student involvement in our undergraduate course in decision theory and Bayesian statistics. Some of the demonstrations involve student participation, while others are essentially lectures with extra class discussion.
Teaching Statistics
A regular component of the Teaching Bits Department is a list of articles from Teaching Statistics, an international journal based in England. Brief summaries of the articles are included. In addition to these articles, Teaching Statistics features several regular departments that may be of interest, including Computing Corner, Curriculum Matters, Data Bank, Historical Perspective, Practical Activities, Problem Page, Project Parade, Research Report, Book Reviews, and News and Notes.
The Circulation Manager of Teaching Statistics is Peter Holmes, [email protected], RSS Centre for Statistical Education, University of Nottingham, Nottingham NG7 2RD, England. Teaching Statistics has a website at http://www.maths.nott.ac.uk/rsscse/TS/.
Teaching Statistics, Summer 1998 Volume 20, Number 2
“The American Statistics Poster Competition” by Jerry Moreno and John Schollenberger
The article covers the history and organisation of the American Statistics Poster Competition, describes the authors' view on what constitutes a statistical poster, and presents a future outlook for the competition.
“Using Spreadsheets to Calculate Prob(X + Y = w)” by John C. Turner
The author describes how spreadsheets can be set up tocalculate the sum of two or more discrete random variableswith arbitrary distributions. From the summary, the authorstates that use of the spreadsheet “allows the student toconfirm properties of the sum of binomial and Poisson randomvariables… In addition, it also allows the student tocompute the probabilities associated with the difference ofrandom variables, and thus find the probability that onerandom variable exceeds another (or exceeds a givenamount).”
“A Probability Game” by Jean Merles
The author describes a simplified form of snakes and laddersthat can be used to initiate an open ended investigation ofprobability. The game provides an opportunity for studentsto experience chance and probability in a situation wherethe theoretical probabilities are not obvious. The game canbe extended using different type of dice and modifying thegame board to have different numbers of squares. Thisallows the instructor to engineer games where analysis ofthe probabilities is relatively simple and then help thestudents generalise to more complex game situations.
“Knock 'm Down” by Gordon Hunt
The author describes a game that engages students incollecting data and interpreting results. “Knock 'm Down” is played with two dice and twelve counters. A shelf ismarked off into 11 sections that are numbered from 2 to 12. Twelve cans are placed on the shelf with no restriction onhow many cans are placed into each section. The game isplayed by rolling two dice, summing the values, and removingall cans from the section of the shelf that has the samelabel as the sum. The goal of the game is to strategicallyplace the cans on your shelf so that you knock off all thecans in the least number of rolls. The author describesthree different approaches that students typically take toidentifying the optimal arrangement of the cans andquestions that can be used to guide students in theirinvestigations. Data collection is motivated by encouragingstudents to compare the results from different arrangements. The author discusses extensions of the activity withprobability modeling and computer simulations.
Topics for Discussion from Current Newspapers and Journals
“Left-Handed Approach to Survival?”
by Ridgely Ochs.Newsday, 24 February 1998, C11.
Ochs reports on a British study in the February issue of theJournal of Epidemiology and Community Health with theimposing title “Is Forced Dextrality an Explanation for the Fall in the Prevalence of Sinistrality With Age?”
Ochs recalls the famous 1981 study by Stanley Coren, popularized in Coren's 1992 book The Left-HanderSyndrome (Free Press). Coren's data showed that, among5147 people ranging in age from 8 to 100, 15% at age 10 wereleft-handed, compared to only 5% at age 50, and less than 1%at age 80. The apparent conclusion is that left-handershave lower survival rates. Coren estimated that the leftyeffect represented a two- to five-year decrease in lifeexpectancy.
Simon Ellis, the author of the new British study, points outthat if Coren is right then the effect is about as large asthe difference in life expectancy between men and women. Heworries that insurance companies might logically be led toquote different rates to left-handers. Ellis' own studylooked at 6097 people aged 15 to 70. He found that theprevalence of left-handers decreased from 11.2% at age 15 to4.4% at age 70. Unlike Coren, Ellis doesn't see a decreasedability of left-handers to survive. Rather, he explainsthat social prejudices against left-handers have forcedthem, over the course of their lives, to switch hands. Inorder to adjust for this, Ellis removed questions aboutwriting and drawing, since these skills are particularlysusceptible to being changed. Still, this didn't completelyremove the lefty effect among older people, and Ellisreports that the case is still not closed.
Ochs did a phone interview with Coren, who said thatPresident Clinton is a lefty, and he suffers bad allergies. Former President Bush is a lefty and suffers from a thyroidcondition known as Graves disease. Ochs observed thatBarbara Bush also has Graves disease, but Coren reportedlydidn't know if Mrs. Bush was left-handed!
“I.Q. Scores are Up, and Psychologists Wonder Why”
by Trish Hall. The New York Times, 24 February 1998, F1.
While SAT scores have gone up and down over the years ‐‐ including one long period of decline from the mid-1960s to the early 1980s ‐‐ it seems that IQ scores just keep goingup. This went unnoticed for a long time because, unlike SATscores, IQ tests are re-normed each year to keep the medianat 100. Political scientist James Flynn discovered thisincrease in the 1980s when he looked at scores on tests donefor the military that had not been normed. This increasehas been called the “Flynn effect.” It is estimated thatsomeone who would have scored in the 90th percentile on the Raven's Progressive Matrices test in the late 19th centurywould score in only the 5th percentile today.
Flynn's observations have been verified by otherresearchers. The American Psychological Association plansto publish an edited volume this spring titled The RisingCurve: Long-Term Gains in I.Q. and Related Measures. Debate continues over the exact cause of the increase. Thelargest gains have been observed for the Raven's test, whichis based on shapes rather than words to minimize theinfluence of culture and education. But some observers havepointed out that children today have much more experienceworking puzzles and mazes, some of which are very close tothe problems used on I.Q. tests.
“US 12th-Graders Miss the Mark”
by Gail Russell Chaddock.Christian Science Monitor, 25 February 1998, p. 1.
This story gives a less encouraging view than the last one. On February 24, the results of the Third InternationalMathematics and Science Study (TIMSS) were announced, andAmerican 12th-graders scored well below the world average. In advanced mathematics and physics, the US ranked last.
This report continues a trend which has seen the US rankingworse at higher grade levels. In a previous test for4th-graders, US students were above average in math andranked second in science. But later, on the TIMSS test of8th-grade students, US students had already dropped belowinternational averages. Now we find the 12th-graderslagging even further behind.
In the past, poor performances have been blamed on the factthat US high schools accept all students, while in othercountries enrollment is selective. This explanation nolonger applies. All 21 countries participating in the TIMSSstudy enroll more than 90 percent of thesecondary-school-age youths. Another explanation held thatUS students suffer from spending far more time watchingtelevision than their peers in other countries. But the TIMSS report showed that US students are now just aboutaverage in number of hours watched per week.
“A Child's Paper Poses a Medical Challenge”
by Gina Kolata.The New York Times, 1 April 1998, A1.
The practice of therapeutic touch is used in hospitals allover the world and is taught in some medical and nursingschools. In this therapy, trained practitioners manipulatesomething that they call the “human energy field.” Themanipulation is carried out without actually touching thepatient's body. Practitioners claim that anyone can betrained to feel this energy field.
Some researchers say that no reliable evidence existsshowing that this technique actually heals patients. Dr. Donald O'Mathuna, a professor of bioethics and chemistryat the Mount Carmel School of Nursing in Columbus, Ohio, hasreviewed more than 100 papers and doctoral dissertations onthis technique without finding any convincing data.
James Randi, a professional magician who is also known as askeptic of some types of alternative medicine, has tried foryears to test the practice of therapeutic touch. So far, only one practitioner has agreed to submit to his test, andshe did no better than chance in detecting the energy field.
The present story is about an 11-year-old Colorado girlnamed Emily Rosa, who was able to recruit 21 practitionersfor an experiment she conducted two years ago. Emily'smother, a nurse who is herself skeptical about the therapy, thinks Emily was successful because practitioners did notfeel threatened by a 9-year-old girl working on a sciencefair project!
For her experiment, Emily placed a screen between apractitioner's eyes and hands, and then held her own handover one of the practitioner's hands. If the human energyfield can be felt, then practitioners should be able toidentify which of their hands Emily held hers over. Emilyconducted 280 tests with the 21 subjects, and theyidentified the correct location of her hand in 44% of thetests.
The results of her study were reported in the Journal ofthe American Medical Association (“A Close Look atTherapeutic Touch, 1 April 1998, pp. 1005–1010). Proponentsof the therapeutic touch technique were quick to dispute thefindings. Meanwhile, Emily received a letter from theGuiness Book of World Records saying she may be theyoungest person ever to publish a paper in a majorscientific journal.
“Risk of False Alarm from Mammogram is 50% over Decade”
by The Associated Press. The New York Times, 16 April 1998, A16.
A new study has concluded that women who have mammogramsevery year for a decade have a 50–50 chance of receiving afalse positive result. The study, conducted over a 10-yearperiod, looked at screening test results for 2400 women aged40 to 69. These women underwent a total of 9762 screeningmammograms and 10905 screening breast examinations, withmedians of four mammograms and five clinical breastexaminations per woman over the 10-year period. If a womenhad a mammogram or breast examination that (1) wasconsidered indeterminate, (2) aroused suspicion of cancer, or (3) prompted recommendation for additional workup, butcancer was not diagnosed within the next year, then the testwas classified as a false positive.
Among the women in the study, 28.8% had at least one falsepositive mammogram, 13.4% had at least one false positivebreast examination, and 31.7% had at least one falsepositive result (breast exam or mammogram). The estimatedcumulative risk of a false positive result was 49.1% after10 mammograms and 22.3% after 10 breast examinations.
The study appeared in the New England Journal of Medicine (“Ten-Year Risk of False Positive ScreeningMammograms and Clinical Breast Examinations,” 16 April 1998,338(16), pp. 1089–1096). You can read the abstract onlineat
http://www.nejm.org/content/1998/0338/0016/1089.asp
In an editorial accompanying the article, Harold Soxconsiders whether the risk of false positives isoverestimated. He points out that an abnormal result wouldbecome a false positive by default if a diagnosis was notmade within a year. But presumably in some of these casescancer actually exists.
On the other hand, a Los Angeles Times article raised thepossibility that the risk may be understated (Thomas H. Maugh II, “Study Warns of Mammogram False Alarms, LosAngeles Times, 16 April 1998, A1). This article observedthat only 6.5% of mammograms from the study showed anabnormality, whereas nationally about 10% of mammograms showan abnormality. The risk of false positives is highest forwomen in their forties, and decreases with age.
“'97 Warmest in Study of Last 600 Years”
by David L. Chandler. The Boston Globe, 23 April 1998, A1.
The last decade has seen some of the warmest years onrecord, and the latest data indicate that 1997 is thewarmest year yet. However, since large scale records forglobal temperature only go back about 100 years, it has beenhard to establish that we are indeed experiencing along-term trend.
A new study by climate researchers at the University of Massachusetts at Amherst attempts to reconstruct climaterecords for the last 600 years. The researchers havesupplemented historical temperature measurements bycollecting data from ice cores, tree rings, and coral reefsfrom over 100 sites around the world. The results have beenpublished in the journal Nature (M. Mann, R. Bradley, andM. Hughes, “Global-Scale Temperature Patterns and ClimateForcing over the Past Six Centuries,” 23 April 1998,pp. 779–787). You can find more details about howtemperature information is derived from such data at the National Oceanic and Atmospheric Administration's web pageon Paleoclimatology:
http://www.ngdc.noaa.gov/paleo/paleo.html
The researchers found warm periods and cold periods over the600 years, but none of the changes compared in magnitude tothe warming that began at the start of the 20th century. While acknowledging that uncertainties remain in their novelapproach, the researchers were pleased to find that theirdata do match historically recorded phenomena such as the “year without a summer” of 1816 (caused by the Tamboravolcano in Indonesia), and the strong El Nino year of 1791. This suggests the method is sensitive enough to pick up evensingle-year climate variations. Furthermore, theresearchers point out that the magnitude of the uncertaintyin their measurements is small compared with the trendsbeing observed.
“Unconventional Wisdom: New Facts and Hot Stats from the Social Sciences. Bearing False Witness to Thy Pollster”
by Richard Morin. Washington Post, 17 May 1998, C5.
Sociologist Stanley Presser of the University of Marylandand his research partner Linda Stinson of the US Bureau of Labor Statistics have found that people exaggerate whenpollsters ask them about their church-going habits.
The two researchers analyzed time-use diaries from themid-1960s, 1970s, and 1990s and compared them to pollingresults obtained by the Gallup Organization and the NationalOpinion Research Center (NORC). The diaries revealed thatthe percentage of Americans who attend church was 42% in1965 and 26% in 1994. By contrast, the Gallup and NORCpolls reveal that the proportion has not changed over thepast thirty years. A 1993–1994 NORC survey reported that38% of its respondents attended mass, a number that hasvaried little since the 1970s.
Presser and Stinson speculate that the discrepancy arisesfrom the way the data were collected. The Gallup/NORC pollsspecifically ask respondents if they had attended religiousservices in the past seven days, whereas the time-usediaries are based on random samples of Americans who wererepeatedly interviewed and asked how they had spent theprevious day. In addition, the researchers suspect that the Gallup/NORC respondents felt the need to impress theirinterviewers, whereas the diary participants were only askedto account for how they spent their time and were unlikelyto have felt the pressure to exaggerate their church-goinghabits.
“Duffers Need Not Apply; Data Show that Good Golfers Makethe Best C.E.O.'s”
by Adam Bryant. The New York Times, 31 May 1998, Section 3, p. 1.
Investment compensation consultant Graef Crystal carried outthis study for the Times. It purports to find a strongcorrelation between the stock performance of major companiesand the golfing prowess of their chief executives. Crystalobtained data on C.E.O.'s golf handicaps from the journalGolf Digest, and used his own data on the stock marketperformance of 51 Fortune 500 companies. He created a “stock performance ranking” which gave each company a scorebased on how investors who held their stock did over athree-year period, with 100 being the highest rating and 0the lowest. Here, reproduced from the article, is Crystal'sdataset.
CEO Company Handicap Stock_Score Melvin_R._Goodes Warner-Lambert 11 85 Jerry_D._Choate Allstate 10.1 83 Charles_K._Gifford BankBoston 20 82 Harvey_Golub American_Express 21.1 79 John_F._Welch_Jr. General_Electric 3.8 77 Louis_V._Gerstner_Jr. IBM 13.1 75 Thomas_H._O'Brien PNC_Bank 7.1 74 Walter_V._Shipley Chase_Manhattan 17.2 73 John_S._Reed Citicorp 13 72 Terrence_Murray Fleet_Financial 10.1 67 William_T._Esrey Sprint 10.1 66 Hugh_L._McColl_Jr. Nationsbank 11 64 James_E._Cayne Bear_Stearns 12.6 64 John_R._Stafford Amer._Home_Products 10.9 58 John_B._McCoy Banc_One 7.6 58 Frank_C._Herringer Transamerica 10.6 55 Ralph_S._Larsen Johnson_&_Johnson 16.1 54 Paul_Hazen Wells_Fargo 10.9 54 Lawrence_A._Bossidy Allied_Signal 12.6 51 Charles_R._Shoemate Bestfoods 17.6 49 James_E._Perrella Ingersoll-Rand 12.8 49 William_P._Stiritz Ralston_Purina 13 48 Duane_L._Burnham Abbott_Laboratories 15.6 46 Richard_C._Notebaert Ameritech 19.2 45 Raymond_W._Smith Bell_Atlantic 13.7 44 Warren_E._Buffett Berkshire_Hathaway 22 43 Donald_V._Fites Caterpillar 18.6 41 Vernon_R._Louckes_Jr. Baxter_International 11.9 40 Michael_R._Bonsignore Honeywell 22 38 Edward_E._Whitacre_Jr. SBC_Communications 10 37 Peter_I._Bijur Texaco 27.1 35 Mike_R._Bowlin Atlantic_Richfield 16.6 35 H._Lawrence_Fuller Amoco 8 33 Ray_R._Irani Occidental_Petroleum 15.5 31 Charles_R._Lee GTE 14.8 29 John_W._Snow CSX 12.8 29 Philip_M._Condit Boeing 24.2 25 Joseph_T._Gorman TRW 18.1 24 H._John_Riley_Jr. Cooper_Industries 18 22 Richard_B._Priory Duke_Energy 10 22 Leland_E._Tollett Tyson_Foods 16 20 Bruce_E._Ranck Browning-Ferris 23 15 William_H._Joyce Union_Carbide 19 13 Thomas_E._Capps Dominion_Resources 18 12 Scott_G._McNealy Sun_Microsystems 3.2 97 William_H._Gates Microsoft 23.9 95 Sanford_I._Weill Travelers_Group 18 95 Frank_V._Cahouet Mellon_Bank 22 92 William_C._Steere_Jr. Pfizer 34 89 Donald_B._Marron Paine_Webber 25 89 Christopher_B._Galvin Motorola 11.7 3Crystal identified the last seven points on the above listas outliers and removed them from the analysis; thisprocedure is described in the article as scientific sifting. The correlation coefficient between stock rate and handicapfor the remaining data points is −0.414. This value is notreported in the article, but Crystal is quoted as saying: “For all the different factors I've tested as possible linksto predicting which C.E.O.'s are going to perform well orpoorly, this is certain the oddest ‐‐ but also the strongest ‐‐ I've seen. There's got to be something there.”
The article raises a number of questions for discussionrelating to data snooping and the treatment of allegedoutliers. For the full dataset, the correlation betweenhandicap and stock rating is only −0.042! There are alsoissues of response bias; it turns out that when GolfDigest asked C.E.O.'s of the 300 largest Fortune 500corporations for their golf handicaps, only 72 replied. (Ofthese, Crystal used the 51 for which he had corporate data.)Finally, while the article clearly presents the findingsquite seriously, some of Crystal's commentary soundstongue-in-cheek. He says of C.E.O.'s, “…if they can gettheir handicap down to 4, why not just pay them an extra 20million bucks?”
“Ask Marilyn”
by Marilyn vos Savant. Parade Magazine, 31May 1998, p. 8.
Marilyn gives the following response to a reader who askedfor an explanation of the margin of error in an opinionpoll.
Good polling is a tricky business, but the guidingprinciple is simple: The larger the sample, themore accurate it is. After much data collection, pollsters have learned their numerical limits ofaccuracy and call them collectively the ‘margin oferror.’ The individual numbers are so consistentthat they are considered standard. For thisreason, the published margin of error on aparticular poll merely tells us the size of thesample. It is based on past polls. For example, if a poll has a margin of error of plus or minus 3%this usually tells us that about 1500 people werepolled. That is, the margin-of-error percentage isassigned to the poll, not developed from it.
Smaller sample have larger margins, and largersamples have smaller ones, but only slightly. Formost purposes, a national sample of 1500 isadequate. In fact, most public-opinion polls usesamples ranging is size from only 1000 to 2000people, but this is amazingly sufficient.
It makes an interesting exercise to sort out what Marilyn istrying to say here.
“Online Voters Get Hankerin' for Anarchy”
by Michael J. Himowitz. The Philadelphia Inquirer, 28 May 1998, F6.
This article gives one more example of how not to do a poll. It describes a poll conducted by People magazine on the Internet that asked on-line readers to vote for the Most Beautiful Person. The winner of the poll was to be featuredin a future print issue of People. In addition to thenames of many well-known celebrities, the ballot alsoincluded a spot to write in a name.
Radio personality Howard Stern suggested that his fans castwrite-in votes for one of his characters on his show ‐‐ Hank, the Angry, Drunken Dwarf. His request generated over 230,000 votes, which made Hank the clear winner. Thisresult points out some weaknesses of this form ofcyber-polling. Of course, there is no reason to believethat the people who write in form a random sample of thepopulation. Here it also appears there was no way tocontrol how many times an individual voted.
“Experts Seek to Avert Asteroid Scares”
by The Associated Press. Chicago Tribune, 7 June 1998, p. 8.
On March 11, front-page newspaper stories reported that Asteroid 1997 XF11 was on a course that would bring it within30,000 miles of Earth in October 2028. That prediction, made by the International Astronomical Union, led to fearsthat the asteroid might actually hit the Earth. Thedepiction of deadly collisions by comets and asteroids inthe Hollywood movies Armageddon and Deep Impact servedto further dramatize the possibilities. However, when thetrajectory of 1997XF11 was recalculated by experts at NASA'sJet Propulsion Laboratory (JPL), it was found the mostlikely path would miss the Earth by 600,000 miles. (Note:this is more than twice the distance to the moon.)
To avoid such sensationalist reporting in the future, scientists are looking for better ways to release theirfindings on asteroids. New discoveries of asteroids headedin our general direction make headlines, but in most casesmore careful calculations subsequently reveal that thethreat is minimal. According to Paul Chodas of JPL, fifteenminutes after he received the XF11 data, his calculationsrevealed that there was “zero threat” to Earth.
In April, NASA proposed guidelines for consultation amongexperts before public announcements. Chodas says that itmight take up to 48 hours for such consultation, and NASArecommended an additional 24 hours before any news release. Earthquake expert Alan Lindh of the US Geologic Survey urgedmore openness about discoveries, as long as the uncertaintyof the initial observations is clearly explained. “Youcan't control the flow of news,” said Lindh, “but you can beas truthful as possible up front.”
The article reports that astronomers have identified 123 potentially hazardous asteroids that could pass within fivemillion miles of Earth and have discovered 200 of theestimated 2000 large asteroids that could pass within 30million miles. You can find more information about asteroidhazards on the NASA Ames web site. The link
http://impact.arc.nasa.gov/news/1998/jun/12.html
has up-to-date information on the 1997XF11 discussion. Related links indexed there include an Asteroid and CometImpact fact sheet, reviews of recent popular books andfilms, and a discussion of whether a meteor could havedowned TWA Flight 800.