“…are regressed on covariates (typically different from those used in the first stage) that are viewed as representing environmental variables. This approach is advocated by Chilingerian and Sherman (2004), Ray (2004), and Ruggiero (2004); published examples include Byrnes et al (1988), Ray (1988Ray ( , 1991, Nyman and Bricker (1989), Aly et al (1990), McCarty and Yaisawarng (1993), Rhodes and Southwick (1993), Banker and Johnston (1994), Chirkos and Sears (1994), Dusanksy and Wilson (1994), Kooreman (1994), Lovell et al (1994), Sexton et al (1994), Chilingerian (1995), Rosko et al (1995), Arnold et al (1996), De Borger andKerstens (1996), Gonza´lez and Barber (1996), Luoma et al (1996), Carrington et al (1997), Gillen and Lall (1997), Burgess and Wilson (1998), Kirjavainen and Loikkanen (1998), McMillan and Datta (1998), Puig-Junoy (1998), Dietsch and Weill (1999), Fried et al (1999a), Garden and Ralston (1999), Cheng et al (2000), Resende (2000), Worthington and Dollery (2000), Chakraborty et al (2001), Mukherjee et al (2001), Raczka (2001), Ralston et al (2001), Isik and Hassan (2002)…”