“…These include Clements and Johnson (1983), Thom (1984, for Ireland), Uri (1986). Selvanathan (1987, 1991), Duffy (1987), Penm (1988), Selvanathan (1988Selvanathan ( , 1989Selvanathan ( , 1991, Heien and Pompelli (1989), Jones (1989a) and Tegene (1990). Selvanathan (1991) reviewed some of these studies.…”