I listened all the way up to the 90s. I have to wonder how this chart is determined. While obviously many of the popular songs of the period trend, there are so

I listened all the way up to the 90s. I have to wonder how this chart is determined. While obviously many of the popular songs of the period trend, there are some places where it doesn't seem right. For example Michael Jackson's Thriller never broke #3, and MJ barely made the top ten week chart until BAD came out. That can't be right. I checked Wikipedia and it says all MJ songs from that album made #1.