IGF1 and central precocious puberty: In addition to being one large study (143 idiopathic CPP girls versus 91 premature thelarche girls), this study is retrospective and uses two different assays to determine IGF1 (IMMULITE Siemens 2000TM before 2013 and IDS-iSYSTM after), explaining why they only use IGF1-SDS values to minimize bias.