Y. Guo, H. Logan, D. Glueck, and K. Muller. BMC medical research methodology, 13 (1):
100(January 2013)7412<m:linebreak></m:linebreak>JID: 100968545; 2013/04/04 received; 2013/07/31 accepted; 2013/07/31 aheadofprint; aheadofprint;<m:linebreak></m:linebreak>Sample size; Dades longitudinals.