- The different tiers pay differently. A free tier has a different royalty rate from a paid tier.
- Interactive vs non-interactive streams. Spotify is an interactive service because the user can select the song she wants to hear so it pays more than Pandora, which is a radio-like service and is therefore non-interactive.
- Different countries pay different rates. The US pays a different rate than the UK, which pays a different rate from Sweden, which pays a different rate from Korea, etc.
Billboard began using this figure last year to help determine chart position, and the music industry has adopted it as a general sales metric.
That said, that 1,500 figure is subject to change. It was 2,000 streams in 2013, so it may be different next year as well.