Co-founder Jo Rice has defended the book's choice of source material on the grounds that "Record Retailer" was the only chart to consistently publish a Top 50 from 1960 onwards. This can be substantiated by the fact that charts published in the "NME" were of a shorter format and other chart listings such as those in "Melody Maker", became less and less informative although they were probably more accurate. Subsequent research has shown that during the "disputed" period of the 1960s, the samples sizes of the "Record Retailer" chart were considerably inferior to those of the other charts: around 30 shops in 1963 in comparison to more than 100 used by "Melody Maker", and later around 80 in comparison to "NME"s 150 and "Melody Maker"s 200. As a result, the placings in that chart were more open to error and manipulation – a situation further worsened by the larger number of records listed in the chart.