The rankings use a 4 year window of matches and weight matches by their importance, e.g. a World Cup match has 4 times the weight of a friendly.
The predictions based on these rankings performed well in an academic study of world football/soccer rankings.
To learn more about the algorithm I developed based on my Ph.D. from Stanford, click here. (The article focuses on American football, but I use the same methods in international football / soccer.)