1. Holt et al. (1996d).
2. McGill (2000).
3. Hedrick (2000), Fredrick and Szymanske (2001).
4. Holt et al. (1970), Sady et al. (1982), Holt and Smith (1983), Prentice (1983), Cornelius and Jackson (1984), Greipp (1985), Wallin et al. (1985), Etnyre and Abraham (1986), Anderson and Burke (1991), McAtee (1993), Holt et al. (1996c), Pelham et al. (2002a).
5. Kabat (1952), Kabat (1958).