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Peter J. Rousseeuw (born 13 October 1956) is a Belgian
statistician A statistician is a person who works with Theory, theoretical or applied statistics. The profession exists in both the private sector, private and public sectors. It is common to combine statistical knowledge with expertise in other subjects, a ...
known for his work on
robust statistics Robust statistics are statistics that maintain their properties even if the underlying distributional assumptions are incorrect. Robust Statistics, statistical methods have been developed for many common problems, such as estimating location parame ...
and
cluster analysis Cluster analysis or clustering is the data analyzing technique in which task of grouping a set of objects in such a way that objects in the same group (called a cluster) are more Similarity measure, similar (in some specific sense defined by the ...
. He obtained his PhD in 1981 at the
Vrije Universiteit Brussel The Vrije Universiteit Brussel (Dutch language, Dutch, ; lit. Free University of Brussels; abbreviated VUB) is a Dutch- and English-speaking research university in Brussels, Belgium. It has four campuses: Brussels Humanities, Science and Engine ...
, following research carried out at the
ETH Eth ( , uppercase: ⟨Ð⟩, lowercase: ⟨ð⟩; also spelled edh or eð), known as in Old English, is a letter used in Old English, Middle English, Icelandic, Faroese (in which it is called ), and Elfdalian. It was also used in Sca ...
in Zurich, which led to a book on influence functions. Later he was professor at the
Delft University of Technology The Delft University of Technology (TU Delft; ) is the oldest and largest Dutch public university, public Institute of technology, technical university, located in Delft, Netherlands. It specializes in engineering, technology, computing, design, a ...
, The Netherlands, at the
University of Fribourg The University of Fribourg (; ) is a public university located in Fribourg, Switzerland. The roots of the university can be traced back to 1580, when the notable Jesuit Peter Canisius founded the Collège Saint-Michel in the City of Fribourg ...
, Switzerland, and at the
University of Antwerp The University of Antwerp () is a major Belgian university located in the city of Antwerp. The official abbreviation is ''UAntwerp''. The University of Antwerp has about 20,000 students, which makes it the third-largest university in Flanders. ...
, Belgium. Next he was a senior researcher at Renaissance Technologies. He then returned to Belgium as professor at
KU Leuven KU Leuven (Katholieke Universiteit Leuven) is a Catholic research university in the city of Leuven, Leuven, Belgium. Founded in 1425, it is the oldest university in Belgium and the oldest university in the Low Countries. In addition to its mai ...
, until becoming emeritus in 2022. His former PhD students include Annick Leroy, Hendrik Lopuhaä, Geert Molenberghs, Christophe Croux, Mia Hubert, Stefan Van Aelst, Tim Verdonck and Jakob Raymaekers.


Research

Rousseeuw has constructed and published many useful techniques. He proposed the
Least Trimmed Squares Least trimmed squares (LTS), or least trimmed sum of squares, is a robust statistical method that fits a function to a set of data whilst not being unduly affected by the presence of outliers . It is one of a number of methods for robust regressio ...
method and S-estimators for
robust regression In robust statistics, robust regression seeks to overcome some limitations of traditional regression analysis. A regression analysis models the relationship between one or more independent variables and a dependent variable. Standard types of re ...
, which can resist
outliers In statistics, an outlier is a data point that differs significantly from other observations. An outlier may be due to a variability in the measurement, an indication of novel data, or it may be the result of experimental error; the latter ar ...
in the data. He also introduced the Minimum Volume Ellipsoid and Minimum Covariance Determinant methods for robust scatter matrices. This work led to his book Robust Regression and Outlier Detection with Annick Leroy. With Leonard Kaufman he coined the term medoid when proposing the
k-medoids -medoids is a classical partitioning technique of clustering that splits the data set of objects into clusters, where the number of clusters assumed known ''a priori'' (which implies that the programmer must specify k before the execution of a - ...
method for
cluster analysis Cluster analysis or clustering is the data analyzing technique in which task of grouping a set of objects in such a way that objects in the same group (called a cluster) are more Similarity measure, similar (in some specific sense defined by the ...
, also known as Partitioning Around Medoids (PAM). His
silhouette A silhouette (, ) is the image of a person, animal, object or scene represented as a solid shape of a single colour, usually black, with its edges matching the outline of the subject. The interior of a silhouette is featureless, and the silhouett ...
display shows the result of a cluster analysis, and the corresponding silhouette coefficient is often used to select the number of clusters. The work on cluster analysis led to a book titled Finding Groups in Data. Rousseeuw was the original developer of the
R package R packages are extensions to the R statistical programming language. R packages contain code, data, and documentation in a standardised collection format that can be installed by users of R, typically via a centralised software repository such a ...
''cluster'' along with Mia Hubert and Anja Struyf. The Rousseeuw–Croux scale estimator Q_n is an efficient alternative to the
median absolute deviation In statistics, the median absolute deviation (MAD) is a robust measure of the variability of a univariate sample of quantitative data. It can also refer to the population parameter that is estimated by the MAD calculated from a sample. For a u ...
(see
robust measures of scale In statistics, robust measures of scale are methods which quantify the statistical dispersion in a sample of numerical data while resisting outliers. These are contrasted with conventional or non-robust measures of scale, such as sample standard ...
). With Ida Ruts and
John Tukey John Wilder Tukey (; June 16, 1915 – July 26, 2000) was an American mathematician and statistician, best known for the development of the fast Fourier Transform (FFT) algorithm and box plot. The Tukey range test, the Tukey lambda distributi ...
he introduced the bagplot, a bivariate generalization of the
boxplot In descriptive statistics, a box plot or boxplot is a method for demonstrating graphically the locality, spread and skewness groups of numerical data through their quartiles. In addition to the box on a box plot, there can be lines (which are ca ...
. His more recent work has focused on concepts and algorithms for statistical depth functions in the settings of multivariate, regression and functional data, and on robust
principal component analysis Principal component analysis (PCA) is a linear dimensionality reduction technique with applications in exploratory data analysis, visualization and data preprocessing. The data is linearly transformed onto a new coordinate system such that th ...
. His current research is on visualization of classification and cellwise outliers. For more information see a 2024 interview.


Recognition

Rousseeuw was elected Member of
International Statistical Institute The International Statistical Institute (ISI) is a professional association of statisticians. At a meeting of the Jubilee Meeting of the Royal Statistical Society, statisticians met and formed the agreed statues of the International Statistical ...
(1991), Fellow of
Institute of Mathematical Statistics The Institute of Mathematical Statistics is an international professional and scholarly society devoted to the development, dissemination, and application of statistics and probability. The Institute currently has about 4,000 members in all parts ...
(1993), and Fellow of the
American Statistical Association The American Statistical Association (ASA) is the main professional organization for statisticians and related professionals in the United States. It was founded in Boston, Massachusetts, on November 27, 1839, and is the second-oldest continuous ...
(1994). His 1984 paper on robust regression has been reprinted in ''Breakthroughs in Statistics'', which collected and annotated the 60 most influential papers in statistics from 1890 to 1990. He became an
ISI highly cited researcher The Institute for Scientific Information (ISI) was an academic publishing service, founded by Eugene Garfield in Philadelphia in 1956. ISI offered scientometric and bibliographic database services. Its specialty was citation indexing and analysis ...
in 2003, and was awarded the Jack Youden Prize (2018, 2022) and the Frank Wilcoxon Prize (2021), the George Box Medal, and the Research Medal of the International Federation of Classification Societies. In 2024, he received the Gottfried E. Noether Distinguished Scholar Award of the
American Statistical Association The American Statistical Association (ASA) is the main professional organization for statisticians and related professionals in the United States. It was founded in Boston, Massachusetts, on November 27, 1839, and is the second-oldest continuous ...
.


Rousseeuw Prize for Statistics

From 2016 onward, Peter Rousseeuw worked on creating a new biennial prize, sponsored by him. The goal of the prize is to recognize outstanding statistical innovations with impact on society, and to promote awareness of the important role and intellectual content of statistics and its profound impact on human endeavors. The award amount is 1 million US dollars, similar to the Nobel Prize in other fields. The first award was presented in 2022.


References

{{DEFAULTSORT:Rousseeuw, Peter Living people 1956 births Belgian statisticians People from Wilrijk Fellows of the American Statistical Association Fellows of the Institute of Mathematical Statistics R (programming language) people ETH Zurich alumni