Chance News 17

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Walking on Water

For the most part, scientists, mathematician and statisticians labor in obscurity. Almost all of what they do is of no interest to the general public. The exception used to be if sex could somehow get connected and then the scientist/mathematician/statistician would suddenly be on the roladexes of the various talk-show programs. As an example, not so long ago a statistical study regarding the size of the ratio of the length of the forefinger to the ring finger was everywhere and anywhere. Why? Because the authors[Nature, 30 March, 2000] claimed there was a statistical significance for the difference of the ratio for homosexuals as compared to heterosexuals. Thus, an easy noninvasive, visual way of spotting sexual preference. The flaws in the study were numerous. The participants were chosen from gay pride celebrations in the vicinity of San Francisco, an area not known to be typical of the United States; multiple comparisons were made and with enough data dredging it is not statistically surprising that there would be the odd comparison that had a p-value less than 5% . The clinical (substantive, practical) significance was more or less zero in keeping with the negligible effect size coupled with measurement error. Nevertheless, titillation was high enough for several weeks of joking, hand comparisons and bad puns by the public and the media.

But sex, while always interesting, has given way to religion in American life. The phenomenal success of Dan Brown's The Da Vinci Code and the rise of the religious right guarantee that any scientific/mathematical/statistical research which can be tied to the Bible will bring instant celebrityhood. Even when the investigation appears in the unlikely Journal of Paleolimnology [2006 35:417-439] and involves "a small freshwater lake (148 km squared and a mean depth of 20 m)." The current name is Lake Kinneret but in Biblical days it was known as the Sea of Galilee upon which Jesus is said to have performed one of his miracles, walking on water. To walk on water is now a phrase that has come into the English language as being synonymous with extra-human, divine talent.

The paper by Nof, McKeague and Paldor is not an easy read, combining as it does analysis based on sea surface temperature, (warm and salty) springs, plume dynamics, ice dynamics and time series. The paper would never have made the talk-show circuit if it were only the typically dry--no pun intended-- presentation in such a technical journal. What sets it apart is its scientific explanation of how Jesus could manage to walk on water. In essence, after much physics, mathematics, and a bit of statistics, the authors have "proposed that the unusual local freezing process might have provided an origin to the story that Christ walked on water. Since the springs ice is relatively small, a person standing or walking on it may appear to an observer situated some distance away to be 'walking on water'." To avoid being inundated by hate mail (which they received in any event) they carefully state, "Whether this [walking on ice] happened or not is an issue for religion scholars, archeologists, anthropologists and believers to decide on."

In essence, the result of most of the highly mathematical argument in the paper is that things were occasionally colder back then and ice could have formed every once in a while, about every 160 years. Strangely enough, much of their data for this allegation comes from two core samples of temperature taken 2000 km away. The justification for this strange assertion is "because this distance is not any greater than the typical weather system scale in this part of the world." They do have some data much closer to the Lake but only from 1986 to 2003 yet "only the first 9 years of data were deemed suitable for use in the subsequent model." Because "the residual plots displayed some wild transitory behavior (as often seen for example, in financial time series data)," so they "added "a GARCH(1,1) component" to an AR(3) model resulting in the prediction of ice formation about every 160 years.

In their summary, the authors carefully state, "We hesitate to draw any conclusions regarding the implications of this study to the actual events that took place...Our springs ice calculations may or may not be related to the origin of the account of Christ walking on water." Nonetheless, Nof and Paldor are not strangers to conjuring up scientific explanations for Biblical phenomena. In 1992 they wrote an article, "Are There Oceanographic Explanations for the Israelites' Crossing of the Red Sea?" [Bulletin American Meteorological Society, 73; 305-314] This time, instead of temperature, it is wind which parted the Red Sea just long enough: "It is suggested that the crossing occurred while the water receded and that the drowning of the Egyptians was of a result of the rapidly returning wave." Nof likened this event to "It's like blowing across the top of a cup of coffee. The coffee blows from one end of the cup to the other." Statistics are completely absent in this paper. However, in 1993 they published a paper, "Statistics of Wind over the Red Sea with Application to the Exodus Question" [Journal of Applied Meteorology, 33, No 8; 1017-1025]. Here they "used the Weibull distribution ...applied to winds in the part of the Indian Ocean adjacent to the Red Sea" to argue that the likelihood of a proper storm would occur "roughly once every 2000 years."

---DISCUSSION---

1. Someone commented that "The reaction among Biblical scholars to Nof's theory ranged from bemused detachment to real irritation." Why the detachment and why the irritation?

2. Were the Israelites lucky to have picked the exactly correct moment? What calculations do you believe they did?

3. What physical phenomenon could explain the destruction of the walls of Jericho? Noah's flood? The Biblical burning bush?

4. The conflict between Darwinism and Biblical fundamentalism has been much in the news the past few years. Why hasn't there been any clash between fundamentalism and aspects of chemistry such as Avogadro's number?

Submitted by Paul Alper

Measuring poverty in London over 100 years

There goes the neighbourhood, From The Economist print edition, May 4th 2006.
Booth redux, From Economist.com, May 4th 2006.

This on-line article uses recent census data to graphically update a 100-year old map of poverty in London by district and street. The original project, led by the shipping magnate Charles Booth, colour-coded every street in the capital according to its social make-up. It shows the extent to which poverty depends on location and how little has changed over the past century.

The article illustrates one area, north Chelsea, in 1898 and 2001, colour-coding each street as either wealthy, well-off, middling or poor. In 1898, Chelsea was socially mixed, neither especially rich nor especially poor. Today Chelsea is considered a very desirable place to live, with many wealthy streets and some of the poverty has disappered. But on closer inspection the Economist claims that

poverty has not been altogether banished from this part of Chelsea, nor has it moved much. Most of the poorest areas in 2001 were also poor in 1898, and in almost exactly the same places. The reason is that the worst Victorian slums have been knocked down and replaced with tracts of social housing.

Neither the original survey nor its updated version use complicated statistical models. In 1898, researchers peered through windows and into back gardens, or asked police officers for opinions, in order to classify each street into one of seven categories from wealthy at the top to 'vicious, semi-criminal' at the bottom of the poverty scale. The 2001 census measures people's socio-economic status as one of eight categories. So to combine the two datasets a subset of four categories was used by the Economist. Having calculated the number of people, within the smallest unit available from the 2001 census, who fall into the four new categories, the single largest group is taken to represent the character of the area.

Further reading

• The Charles Booth Online Archive is a searchable resource giving access to archive material from the Booth collections of the British Library of Political and Economic Science (the Library of the London School of Economics and Political Science) and the University of London Library.
• Poverty maps of London - this interactive webpage allows viewers to zoom in on an area of London to see the original 1898 map juxtaposed with a modern view of the same area.
• 2001 UK census

Questions

• The Ecomonist gives an example of it classification methodology: if an output area contains 80 members of the upper managerial and professional class 'the wealthy' and 60, 40, and 20 members, respectively, of the other three new categories, it is taken to be wealthy. Is it reasonable to based the classification of an area on the most common category of resident? e.g. should the number of people in each steet be taken into account?
• How might missing data be handled, old streets that have disappeared or new streets that didnt exist in 1898?

Submitted by John Gavin.