Prodyot Kumar Bhattacharya passed away March 9, 2018, at his home in Davis, California. He was professor emeritus at the University of California at Davis and contributed to the field of statistics during a career that spanned more than 50 years.

PK, as he was called by many colleagues and friends, entered Presidency College, Kolkata, to earn his bachelor’s degree in statistics, and ultimately received his master’s degree and PhD under the supervision of H.K. Nandi from The University of Calcutta. In 1960, he traveled to the United States and held postdoctoral positions at The University of North Carolina at Chapel Hill and Stanford University. After a brief period at the Indian Statistical Institute (ISI) in Calcutta, he returned permanently to the US in 1965 upon accepting a position at the University of Arizona. He spent sabbatical terms at the University of Minnesota, ISI, and Massachusetts Institute of Technology. In 1980, he left Arizona to help establish the UC Davis Division of Statistics, where he remained until his retirement in 1994—though his contributions to statistical science continued until 2016.

Prabir Burman and Debashis Paul, in an obituary they wrote for the IISA, credit PK with being “instrumental in developing a well-balanced and rigorous graduate program in Statistics at UC Davis.” Describing his teaching, they say he was “unusually gifted, with his ability to convey even the most difficult concepts and topics by breaking them down in understandable, short and logically connected pieces.” Even after retiring, he continued to teach a Ph.D. level mathematical statistics course for many years at the request of the Statistics Department. Theory and Methods of Statistics, PK’s lecture notes for advanced graduate students and research statisticians, co-authored with Prabir Burman, was published in 2016.

PK’s early seminal work, published in the Annals of Mathematical Statistics in 1966, proposed a uniformly superior estimator for the mean of a multivariate normal vector under unknown variance and generalized loss function, an important expansion on Charles Stein’s surprising result showing inadmissibility of the ordinary least squares estimator in dimensions exceeding two. Throughout his career, PK maintained special interest in nonparametric estimation functions and change-point analysis, an area that led to demonstrating the large sample behavior of the maximum likelihood estimator of an unknown change-point through a Brownian motion process with drift. His research was motivated by unusual problems across a spectrum of disciplines. Of particular note, his collaboration in a cosmological application led to a nonparametric inference method for a regression model having errors with infinite variance and a truncated response, an approach that reconciles the red shift effect of a light source in an ever-expanding universe and the truncation arising from the low luminosity of distant objects. The method allows analysis and interpretation of complex astronomical data, such as those collected by the Hubble Space Telescope.

PK was honored with a special volume of contributed papers by colleagues and former students in 2012: Nonparametric Statistical Methods and Related Topics: A Festschrift in Honor of Professor P.K. Bhattacharya on the Occasion of His 80th Birthday (World Scientific, edited by J. Jiang, George Roussas and Frank Samaniego).

PK Bhattacharya was born on September 30, 1930, in Calcutta (Kolkata), India. The fourth of six children, he lost his mother and younger sister when he was a young boy. Despite hardship at an early age, he found joy in the books he discovered at the local Boys’ Own Library. He developed a special fondness for Bengali and English poetry and, for the rest of his life, could recite from memory the verses that moved him during his school days. He loved popular and classical Indian and western music, all kinds of food and spirits, and traveling to all corners of the world. He was happiest when sharing these lifelong passions with others, whether it was setting out his favorite selection of cheeses, introducing his grandchildren to classic movies, or attending an opera performance in San Francisco or New York.

PK left an indelible mark on science and the lives he touched through his intellect, humor, generosity, and spirit of adventure. He is survived by his wife of 54 years, Srilekha; his daughters, Suparna Jain and Aparna Anderson; and his grandchildren, Arjun and Anjali Jain and Anil and Mira Anderson.

Written by Aparna Anderson, Statistics Collaborative, Inc., with contributions from Prabir Burman and Debashis Paul, University of California at Davis