“…The main OPAL project report (Andrade et al, 2011) and related papers by Ehlers and Conole (noted above) continue to be cited widely by researchers in OEP (see Armellini & Nie, 2013;Atenas, Havemann & Priego, 2014;Carey, Davis, Ferreras & Porter, 2015;Casey & Evans, 2011;Coughlan & Perryman, 2015;Cronin, 2017;Czerniewicz et al, 2017aCzerniewicz et al, , 2017bHogan et al, 2015;Karunanayaka, Naidu, Rajendra & Ratnayake, 2015;Masterman, 2016;Murphy, 2013;Nascimbeni & Burgos, 2016;Paskevicius, 2017;Smyth, Bossu & Stagg, 2016).…”