A while back, we were discussing the fact that the 1990s saw a huge leap in the number of songs that spent weeks and weeks at Number One on the pop charts, and OPC commenter Joe suggested that the changeover to the SoundScan system of accounting may have been a prime driver of this. I have now found that this phenomenon is entirely due to SoundScan.
Consider: Billboard went to the SoundScan method on November 30, 1991. Prior to that date, 25 songs had hit Number One in 1991 (it had been 25 in 1990, as well). In 1992, only 12 songs went to Number One; in 1993 it was down to 10, and in 1994 it went down to nine.
In early 1975, there was a period of 13 weeks where there was a new Number One song every week, from "Mandy" to "Philadelphia Freedom." (Elton John broke the string by staying on top for a second week, on the April 19, 1975, chart.) Now it takes a whole year (or more) to have 13 different Number Ones.
I have to say, this seems to be a change for the worse, for both Billboard and for the music industry, which seems to have endured many such self-inflicted wounds over the years. If you have Number One hits changing on a regular basis, you create interest in the pop charts, and in Casey Kasem or Shadoe Stevens or whomever, and maybe even in listening to the radio. Having "Un-Break My Heart" stay at Number One for 11 straight weeks doesn't create much of anything. And it's not like this is some sort of highly technical operation with an exact correct number, like measuring the temperature on Venus. As I understand it, the charts used to be based on record sales and airplay, and Billboard was entitled to calibrate airplay any way it liked. It's not exactly going to foster a congressional investigation if Billboard fiddled with its rankings again to increase chart movement. At the present time, does anyone really care about the pop charts? I can't say that I do.