20th centuryIntroductionThe 20th century is characterized by some major methodological battles. Firstly there is a disagreement with regard to the preference for correlational large scale studies (Karl Pearson) versus experimental small scale studies (Ronald Fisher). The field of experimental small scale studies witnesses the emergence of a second controversy: H_{0} testing (Ronald Fisher) versus the inclusion of H_{1} and the concept of Power (Jerzy Neyman & Egon Pearson).Spearman's belief in one general intelligence (g) factor, which supposedly was the driving force behind the development of factor analysis, leads to arguments, which last for several decennia, with Thurstone and others who gradually look upon factor analysis as 'just' a way to simplify the data. After the second world war nonparametric analysis booms and the invention of the computer creates numerous possibilities for implementing new (and old) ideas such as multidimensional scaling, bootstrapping and multivariate analysis. 

1900  Karl Pearson presents the idea of the Chi square distribution 
1904  Charles Spearman lays the basis for Factor analysis and completes it 8 years
later.
Spearman presents the correlation coefficient for rank data. 
1908  William Gosset
presents his work on the t distribution and the application of the t test. The first appearances of the t test in psychology and related areas are in the early 30s, but Shen (1940) still refers to the t test as not yet in general use in the field of education 
1925  Ronald Aylmer Fisher publishes his Statistical methods for research workers. It is the first textbook presentation of analysis of variance. 
1933  Andrei Kolmogorov presents an axiomatic basis for probability in his book Grundbegriffe der Wahrscheinlichkeitsrechnung (Foundations of the Calculus of Probabilities). He also introduces the test statistic F_{n}(x)  F_{0}(x). 
1933  Harold Hotelling publishes his work on principal component analysis 
1939  Vladimir Smirnov uses the statistic developed by Kolmogorov to construct the KolmogorovSmirnov test 
1945  Frank Wilcoxon presents the the ranksum test and the signedrank test 
1976  Gene Glass publishes his article on combining the results of multiple studies and coins this approach metaanalysis. Although many of these ideas existed long before (Lush 1931, Fisher 1932; Pearson 1933, Snedecor 1946) it is Glass who gives this approach the impetus to achieve the status it enjoys since. 
1977  John Tukey presents exploratory data analysis (EDA) as an antidote to the ritualized testing of hypotheses instead of first looking at the data 