The large body of observations extant from pre-telescopic East Asia - China, Japan and Korea - provide the opportunity to investigate the behaviour of the Sun and solar system over a much longer period of time than that since telescopic observations began in Europe. Much past work in this field has tended to concentrate on individual records of particularly significant observations. In this study the variations in the frequency of the observation of meteors, comets, eclipses, planetary conjunctions and occupations, sunspots, and aurorae during the pre-telescopic period are examined in contemporary records from these three countries. It is to be expected that data artefacts (frequency variations not of astronomical origin) are present to some degree in early sources. The records are translated and collated where necessary, and by comparing patterns across the three countries and across different types of event several major data artefacts are identified and classified. The problem of such artefacts has not previously been the subject of analysis. The results of this study are therefore of significance in considering the reliability of these sets of data for the examination of long term variations in the solar system.