Complex sentence: By 2003, the Icelandic Heathen organisation Ásatrúarfélagið had 777 members, by 2015, it reported 2,400 members, and by January 2017 it claimed 3583 members, constituting just over 1% of the Icelandic population.
Split into simpler sentences: By 2003, the Icelandic Heathen organisation Ásatrúarfélagið had 777 members, and by 2015, it reported 2,400 members. As of January 1st, 2017, members of Ásatrúarfélagið are 3583, just over 1% of the Icelandic population.