“…Moreover, a group may have more influence at one time than at another time, or book a 33 For a negative effect, see Miller (1991), Plotnick (1986), Trefler (1993), Young (1991), fbr a positive effect, see, e.g., Abler (1991), Becker (1986), Boucher (1991), Congleton and Shugart (1990), Kristov et al (1992), Leigh (1994), Pincus (1975), Renaud and Van Winden (1991), Stigler (1971), for ambiguous or insignificant effects, see Graddy and Nichol (1989), Michaels (1992), Neck and Schneider (1988), Nelson (1982), Renaud and Van Winden (1988), Salamon and Siegfried (1977).…”