Piet Groeneboom, Jan van Mill, Aad van der Vaart Statistics as both a purely mathematical activity and an applied science NAW 5/18 nr. 1 maart 2017 55 Piet Groeneboom Jan van Mill Aad van der Vaart Delft Institute of Applied Mathematics KdV Institute for Mathematics Mathematical Institute Delft University of Technology University of Amsterdam Leiden University [email protected] [email protected] [email protected] In Memoriam Kobus Oosterhoff (1933–2015) Statistics as both a purely mathematical activity and an applied science On 27 May 2015 Kobus Oosterhoff passed away at the age of 82. Kobus was employed at contact with Hemelrijk and the encourage- the Mathematisch Centrum in Amsterdam from 1961 to 1969, at the Roman Catholic Univer- ment received from him, but he did his the- ity of Nijmegen from 1970 to 1974, and then as professor in Mathematical Statistics at the sis under the direction of Willem van Zwet Vrije Universiteit Amsterdam from 1975 until his retirement in 1996. In this obituary Piet who, one year younger than Kobus, had Groeneboom, Jan van Mill and Aad van der Vaart look back on his life and work. been a professor at Leiden University since 1965. Kobus became Willem’s first PhD stu- Kobus (officially: Jacobus) Oosterhoff was diploma’ (comparable to a masters) in dent, defending his dissertation Combina- born on 7 May 1933 in Leeuwarden, the 1963. His favorite lecturer was the topolo- tion of One-sided Test Statistics on 26 June capital of the province of Friesland in the gist J. de Groot, who seems to have deeply 1969 at Leiden University. north of the Netherlands. He was the el- influenced Kobus outlook on mathematics. After his graduation Kobus spent a year dest of three sons of Wijbo Jacobus Oos- During his student days he married Käthe as a visiting assistant professor at the terhoff and Gerarda Elisabeth Johanna Oos- Hötte, with whom he was to share the rest University of Oregon in Eugene, where he terhoff-Hoefer Wijehen. The Second World of his life and to have two sons, Wijbo became friends with Don Truax (who was War broke out during his early school days, and Rutger; his eldest was born before his professor of Statistics there) and his fam- but Kobus escaped famine and other war graduation. ily. In 1970 he was appointed as ‘lector’ miseries, as his father had sent him to his at the (then) Roman Catholic University of uncle’s farm, while himself continuing his Career Nijmegen, and then in 1975 as full profes- practice as a lawyer in Leeuwarden. From 1961 on Kobus was employed at the sor in Mathematical Statistics at the Vrije After the war Kobus attended the Ste- Mathematisch Centrum in Amsterdam (now Universiteit Amsterdam, a position he held delijk Gymnasium in Leeuwarden (a top CWI), as an assistant until he obtained his until his retirement in 1996. It is ironic that level high school with a curriculum that master in 1963, then as a ‘medewerker’, Kobus switched from a catholic to a prot- includes ancient Greek and Latin), where and from 1967 to 1969 as the deputy-di- estant university, being not at all religious he graduated in 1951 in the science (‘beta’) rector (‘sous-chef’) of the department of himself. Nowadays both universities have track. He next started studies in geogra- Mathematical Statistics. The head of this a general outlook, but this was different phy at the University of Amsterdam, in line department was J. Hemelrijk, and the Math- in the 1970s. The Vrije Universiteit had to with a passion for traveling and collecting ematisch Centrum was a thriving place for grant Kobus official (and rare) dispensa- minerals that he maintained throughout both applied and mathematical statistics. tion from endorsing the Christian objec- his life. However, he switched to mathe- Kobus was involved in consulting projects tives of the university, and demanded him matics, in which he obtained his ‘kan- and also worked on a PhD thesis. In his to write a statement that he would respect didaatsdiploma’ in 1959 and his ‘doctoraal - thesis Kobus acknowledges the regular the protestant character of the university. 56 NAW 5/18 nr. 1 maart 2017 Statistics as both a purely mathematical activity and an applied science Piet Groeneboom, Jan van Mill, Aad van der Vaart in 1977. Kobus enjoyed working with stu- dents, and was an encouraging teacher. Although he left his students free to pur- sue whatever subject they chose, he read every word of their dissertations, and his preference for exact and clear expression made him want to rewrite every sentence. Later he more than once jokingly claimed that perhaps Richard Gill had taught him survival analysis, but certainly he had taught Richard (a native speaker of course) to write correct English. A typical feedback might start with saying “You make people work so hard. Why don’t you give more explanation!”, but would quickly turn into positive comments. The Mathematisch Cen- trum also organised courses, usually one week long, for mathematicians, also from Belgium. Kobus was involved in two such courses: one on contiguity and efficiency of rank statistics, and one on efficiency of tests and large deviations (with Piet Groe- neboom and Rob Potharst as lecturers). These were important topics of research at the time; the second was the topic of the theses of three of Kobus students. Music Kobus played the violin in his youth, and was interested in music, both classical music and jazz. Piet knows this because Kobus told him, but his sons do not re- member having heard him play. Piet still remembers the following events, which he considers somehow typical for his relation- ship with Kobus. During the big ISI con- gress in Amsterdam in 1985 a ‘gathering of friends’ (Kobus, Henry Daniels, Ronald Pyke, Jon Wellner and Piet) was planned at Piet’s house in the town Utrecht, which is about an hour’s drive from Amsterdam. It was a day of extreme rainfall, which made driving difficult. The plan was that Kobus Photo: Andrew S. Tanenbaum Andrew Photo: would take some of the friends in his car Kobus Oosterhoff in 1998 and Piet the remaining persons, and that they would meet at the first gasoline sta- Kobus always kept to this promise, which isticians in the Netherlands, and Kobus tion on the highway from Amsterdam to was made easy by the fact that his politi- returned to the Centrum as an advisor in Utrecht, after which Kobus would follow cal ideas were in tune with Christian ethics 1971, a position he kept until 1981. In this Piet to his house in Utrecht. Piet waited and his colleagues in the mathematics de- capacity he became PhD advisor to Richard for a long time at the first gasoline station, partment were liberal, even if in majority Gill and Piet Groeneboom, who were ap- but did not see his PhD supervisor appear. adhering to the religious character of the pointed at the Centrum and both obtained He reluctantly got out of the car into the university. On occasions such as a PhD de- their PhD in 1979. They were the second heavy rain to call Kobus’ wife from the sta- fense, where the chair person had to pro- and third of eight doctoral students under tion (pre mobile phone time!), but she also nounce a prayer, Kobus would have him- Kobus guidance, all defending at the Vrije had absolutely no idea where her husband self replaced for this part of the ceremony. Universiteit. The first student was Wilbert could be. What had happened was that Ko- The Mathematisch Centrum in Amster- Kallenberg, who had started with Kobus bus had taken a second entrance to the dam remained a meeting place for stat- in Nijmegen and defended in Amsterdam highway, missing the first gasoline station. Piet Groeneboom, Jan van Mill, Aad van der Vaart Statistics as both a purely mathematical activity and an applied science NAW 5/18 nr. 1 maart 2017 57 Anyway, the group gathered at the second isca de Gunst), enabling them to travel and was one of the best compliments to him gasoline station (close to Utrecht), and to develop in teaching and research, and ever given. everybody finally arrived at Piet’s house. pointing out less obvious details of aca- Kobus was full of ideas, especially on Ronald Pyke then said: “Henry and Piet, demic life. new education plans. He was dean when in why don’t you play something for us?” And 1990 the study program Bedrijfswiskunde Henry Daniels immediately set himself at ‘Algemene Statistiek’ en Informatica (now Business Analytics) the piano, after which it was decided that At the time of his appointment at the Vrije was founded at the Vrije Universiteit. It be- Händel’s famous and beautiful D major Universiteit in 1975, the department of came a great success, although co-founder sonata for violin and continuo would be mathematics there was on its way to find- Gerke Nieuwland once jokingly complained played. Henry’s favourite instrument was ing a balance between theoretical and ap- that Kobus together with Bert Kersten had a British invention, the concertina (a kind plied mathematics. There had been recent turned his concept of a modern informa- of accordeon), but he also was an excel- appointments in applied analysis and nu- tion-technology-based mathematics into lent pianist. Piet met Kobus again the next merical mathematics, and computer science mere applied statistics. In later years Ko- morning and Kobus told him: “I did not was developing. Although he also taught bus was thinking about how mathematics exactly have high expectations of how this pure mathematical statistics courses, some could be integrated with life sciences in was going to be with Henry and you, but advanced, Kobus naturally weighed in on order to attract more students, and worked to my relief it was actually pretty nice, I the applied side.