I think Linda Carol once wrote an article explaining why the same amount of reads could result in different earnings at different times of the year. It had to do with how many other articles these readers are going through. It would make sense that, in December, with more people busy with the holidays, most people spent less time on Medium, and thus the earnings generated per reader per reading were higher than in January. In January, people got back to business as usual and Medium as usual, reading more, and writers being paid less....? I know you have the same amount of reads, but surely those could be different readers than what you had in December. Just saying, money coming from different readers with various interests and reading habits...?