How does Spotify creates ''top tracks of 20XX'' type playlists?

[xara-3]

and I'm not talking about top tracks playlist for a certain country. Just curious in general. Is the selection criteria of songs based on:

1. how many times certain songs were played in a year on Spotify?

2. how many times people added these songs on their playlists or saved/ favorited them?

3. is there an external index involved as well (such as the billboard) that helps certain songs be included in these playlists around the end of year

[osornios]

Hey @xara-3 

I guess your question can only be answered by someone from Spotify, but I would think the number of streams is the most important metric. 🙂