1. Altman DG (1980) Statistics and ethics in medical research: III. How large a sample. Br Med J 281:1336–1338
2. Altman DG (1997) Relation between several variables. In: Altman DG (ed) Practical statistics for medical research. Chapman & Hall/CRC, Boca Raton pp 325–361
3. Bakker EWP, Koning JCMF, Verhagen AP, Koes BW (2003) Interobserver reliability of the 24-hour schedule in patients with low back pain. JMPT 26(4):226–232
4. Bakker EWP, Verhagen AP, Lucas C, Koning JCMF, Haan de RJ, Koes BW (2006) Daily spinal mechanical loading as a risk factor for acute non-specific low back pain. Eur Spine J (epub ahead of print)
5. Chavannes AW, Mens JMA, Koes BW, Lubbers WJ, Ostelo R, Spinnewijn WEM, Kolnaar BGM (2005) NHG-standaard lage rugpijn. Huisarts Wet 48(3):113–123