Carobene A, Guerra E, Marques-Garcia F, Boned B, Locatelli M, Coşkun A, Díaz-Garzón J, Fernandez-Calle P, Sandberg S, Aarsand AK, , Clinica Chimica Acta, , , European Biological Variation Study (EuBIVAS): within- and between-subject biological variation data for serum morning cortisol based on weekly samplings from 91 healthy participants