Why was the all-time chart methodology revised?
The same methodology that provided a fairly balanced list with hits from all eras on the 1994 chart skewed heavily toward the ’90s when that same formula was employed for the Hot 100’s 40th Anniversary. To wit, every single title in the top 10 of the 1998 chart had been released since 1991, while earlier decades had less representation on that 1998 recap than was seen on the 1994 all-time chart. That shift toward newer songs happened during that four-year interval because the 1991 advent of sales tracking from Nielsen SoundScan and radio monitoring by Nielsen Broadcast Data Systems allows big hits to spend more weeks in the top 10, and more weeks on the overall chart, than happened in the earlier years when the chart was based on surveys of retailers and radio programmers. For the Hot 100’s 50th Anniversary, Billboard’s charts department ensured a more balanced representation of hits from all 50 years, by analyzing the length of chart runs in earlier decades, as well as the average wee
