The quality (accuracy and reliability) of data published in the Soviet Union and used in historical research is another issue raised by various Sovietologists.[26][27][3][4] The Marxist theoreticians of the Party considered statistics as a social science; hence many applications of statistical mathematics were curtailed, particularly during the Stalin era.[30] Under central planning, nothing could occur by accident.[30] Law of large numbers or the idea of random deviation were decreed as "false theories".[30] Statistical journals and university departments were closed; world-renowned statisticians like Andrey Kolmogorov or Eugen Slutsky abandoned statistical research.[30]