Wednesday, 27 May 2009

Measuring and comparing risks

Yesterday's newspaper had a feature about the risks associated with competing in a triathlon. A study presented to the American College of Cardiology Conference had reported that the death rate among competitors in triathlons was about twice that of competitors in marathons. (1.5 per 100,000 competitors compared with 0.8). That news report closed with the comment from one of the staff at my university that the idea that exercise is dangerous should be compared with sedentary life.

O.R. professionals ought to be able to see through the nonsense of the report and the comment. What are you trying to measure? How do you compare one activity with another? The death rate in the U.K. is about 1 per 100 per year, or 1000 per 100,000. Dividing that by 365 and then by 8, we get 0.35 per 100,000 in a three hour period. So the death rate in marathons (which last 3 to 4 hours for the majority of competitors) is about twice the national death rate. But the rate varies with age and gender and lifestyle. However, the national death rate includes deaths from accidents, which generally affect the more mobile sectors of the population. The people who die outside marathons include the terminally ill, the aged, etc. -- not the sort of people who compete in endurance sport. They probably have an extremely small chance of dying of natural causes in the next three hours. But they have that risk of accident. So we can conclude that the person who decides to enter an endurance sport increases their chance of dying during that event. But the actual risk is still very small; the half-marathon that I mentioned earlier has about 2500 competitors. If the figures for marathons and half-marathons are comparable, there will be an avaerage of one death every fifty years.

But, even more seriously, the reports about when the deaths occur in triathlons, as all but one of those recorded were in the swimming sport, should alert organisers to warn the competitors about the risks of not being prepared for a long, frantic swim in water that is colder than in heated swimming pools.

As for me, I shall cycle home today. My risk of an accident is about 1 in 4000 based on an average of 1 accidents per ten thousand person miles (here) and a journey of 2.5 miles home. (This is about my experience -- I have been hospitalised three times in 40 years of cycling, with an average annual mileage of a little over 1000 miles, giving 3 accidents in 40,000 miles.)

Monday, 18 May 2009

Displaying data provocatively

For many years, I have been interested in the potential for using O.R. in developing countries. By a process of serendipity, I have just discovered Gapminder, where data about the world's nations are shown in original and challenging ways. I wish that I had discovered the site before now!

Wednesday, 13 May 2009

Spreadsheets and O.R.

The journal Interfaces from the U.S. O.R. Society (INFORMS) is one that I have always enjoyed reading. It describes itself as the "Journal on the Practice of Operations Research" and has often published detailed descriptions of case studies. Older members of the O.R. community will recall that for many years it was edited by Gene Woolsey, and he contributed anecdotes about his practical experience; it wasn't always the received wisdom of O.R. academics, but it was based on genuine experience of getting ones hands dirty doing our discipline.

The March-April 2009 issue of Interfaces has arrived (it takes time to cross the Atlantic) and includes an article "How Electronic Spreadsheets Changed the World" (Rick Hesse and Deborah Hesse Scerno). There was a great deal to which I could relate, as we ran a spreadsheet modelling course in the degree programme in Mathematical Statistics and O.R. at Exeter University. (From the launch of the programme, we taught students to write simple programs in Fortran, then Pascal, Simula and Smalltalk. I recall telling applicants that we expected them to use computers as a tool to help them solve problems, so we stressed a thoughtful approach to programming, and the willingness to use computer packages sensibly.)

Spreadsheets came on the scene in the 1980's -- and provided many companies and individuals with a reason for buying a personal computer. Then spreadsheets were used in schools, with the result that university entrants and others joining the job market had a basic knowledge, often of Excel. But that basic knowledge did not extend to much model-building. We found that we needed to share ideas from computer programming with students in order to help them build appropriate models. As the article emphasises, spreadsheets are wonderful -- used in the right fashion. And O.R. people need to recognise that their fashion is different from that of other professionals, and so their spreadsheet skill set needs to be honed suitably. And that takes time!

Tuesday, 5 May 2009

Running a sponge station

Google can't find the expression "Running a sponge station", so this is a first!

On Sunday 3rd May, our church ran a sponge station for the Great West Run, which is Exeter's half marathon. You can see our church at 1:41 on the video, and just glimpse some of our sponge station roadies in the next two seconds.

Our job was to hand out damp sponges to runners as they passed, and we were equipped with cheap sponges, bins for water, tabards to wear. After that, we were on our own. With experience from 2008, we had buckets and large jars for water as well, and the church tap was running continuously to refill the bins. We needed a team to collect discarded sponges, which were then washed (my job) and returned for reuse as the runners passed the church four times!

There is an assignment problem here, dealing with the varied jobs that need to be done; moving water, collecting sponges, washing, handing out. Unfortunately, it is a messy problem to solve. I don't know the skills of the volunteers, and the demands on the team in fiture will depend on the weather! So, like so many messy problems, it was solved dynamically, as each of us who could transferred between tasks as required.

At the end, we had shown God's love for the community.


Not much about O.R. today. It has been the Bank Holiday weekend in the U.K., but for Tina and myself, it has been our wedding anniversary party. We celebrated 33.3333 years since we got married on an overcast day in December 1975. We decided to mark one third of a century for several reasons, but most imporatnat, it moved the anniversary to late spring, and, hoepfully, good weather, and the opportunity for friends to travel to be with us.

On Friday evening, our church hosted a concert by the Exmouth Town Concert Band in aid of charity, and we had requested two items which had been played at our ceremony. The first was the theme from the film "The Dambusters", the second was Grieg's "Morning" from the Peer Gynt Suites. Our ceremony included a hymn written in the early 1970's to be sung to the film tune, but it was not well known then. So John, our organist, included it in the voluntary before the service. We heard later that many in the congregation had expressions on their faces showing their gradual recognition of the tune, and also their surprise at its use in the voluntary. Later, those faces showed even more surprise as our guests realised that they were going to sing to that music. We wish we had had eyes in the backs of our heads to see the congregation. John had also suggested, wisely, that the music before the service should be selected by myself and Tina's mother, as Tina herself would not be there to hear it!

On Saturday we hosted a party in the garden for about 60 friends and family. The sun shone, the food and drink were there in plenty, and everyone seemed to enjoy themselves. Thanks to my brothers, sisters-in-law and nephew, Tina and I were free to circulate. In my welcome, I realised that the most appropriate word to describe the fact that everyone knew us, but nobody else knew everyone else, was the mathematical term intersection -- so I used it! Apart from that, the only O.R. related part of the day was the need to schedule the preparations of garden, food and ourselves, and that had to be done dynamically!

One unexpected aspect of such a gathering was the way that several people had known us very closely at different times in our lives and in different circumstances, and such people had the opportunity to share their memories with others. So a friend from undergraduate days discovered how different I had seemed when I embarked on a postgraduate course at a different university, and friends from Exeter discovered varied aspects of our lives.

Then we had a small, intimate supper for family and one couple whose love and support has meant a great deal to us over more than 33.3333 years.