Did the statistician Egon Pearson have a PhD? If not, to what extent did he write a dissertation?
A biography of Egon Pearson from the Royal Society covers his education this way:
After finishing his school education at the Dragon School, Oxford, and Winchester College, E. S. Pearson would have liked to join up in the summer of 1914, but was considered by his father hardly fit enough physically, and went somewhat reluctantly to Trinity College, Cambridge, being admitted as an Entrance Scholar on 25 June of that year. His tutor was Mr Whetham (afterwards Sir William Dampier), and he obtained a First class in Part I of the Mathematical Tripos at the end of his first year, in spite of being quite ill for a time. Still anxious to do something useful for the war effort, he obtained a post at the Admiralty and then the Ministry of Shipping. This war service enabled him to qualify for his B.A. in 1920 (and M.A. in 1924) by taking a further approved course of study.
There is no mention of a doctorate, or any thesis work. This was not uncommon in much of the 20th century. A PhD was not a requirement to be a professor for quite some time.
Now, as noted by @njuffa in comments, his tagline in publications changed from M.A. to D.Sc between 1925 and 1926, several years after getting his masters. By 1926 he had published 8 papers, which is a pretty good output for a Ph.D student (note njuffa's pointer to what a D.Sc. represents). And it is a bit curious that the Royal Society biography would not mention it.