What does Billboard's Hot 100 measure?

In it's current form, just what does Billboard's Hot 100 truly measure?

While it does sometimes happen to coincide with what song is truly the most popular in the nation at a given time, more often than not, it doesn't. Songs such as Leona Lewis' "Bleeding Love" were multi-format #1's and sold lots of singles and albums over a long period of time and obviously were worthy of the peak position...

Other songs have only reached the #1 position on that chart thanks to the repression of downloads (i.e: Rihanna, Mariah Carey), while still others have peaked at #1 there thanks to lots of downloads/sales by a fanbase (i.e: multiple American Idol artists).

Other artists, such as Taylor Swift and the Jonas Brothers have had new songs sell a lot of units the first week and then drop off dramatically in the following weeks, often resulting in a top 10 debut and a drop outside of the top 40 within a week or two. Was it a song's popularity that made these songs sell a lot, or was it fanbases?

Still other artists such as Kid Rock are victims of the chart's methodology thanks to the chart having a bias against songs that aren't available for individual sale. Kid Rock's recent hit "All Summer Long" peaked at #23 on the chart despite being top 5 at three different formats. Since there was no single available for download it received ZERO Hot 100 sales points. The latter despite the fact that people were flocking to stores to buy his Rock N Roll Jesus album to the tune of over 100,000 units a week at the song's peak.

We also have a special case with Estelle's recent hit, "American Boy." This song was at #11 on the Hot 100 when the label decided to pull the single in an effort to move albums. The song dropped to #37 on the Hot 100 the next week. Did the song suddenly lose popularity? I think not. Shortly thereafter, "American Boy" became available again and voila, it ended up "rebounding" into the top 10 of the Hot 100.

The above said, what does the chart actually measure? If you know, please respond with a comment!

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