“…Working from a premise that sensitivities to stressors vary among species and biotic groups, a variety of numerical stressor‐specific biotic indices have been developed and are used to aid interpretation of the causes of biological degradation of fresh waters. For some time, indices have been based on perceived tolerance of organisms to pollution as assessed by expert judgement, such as ASPT, LIFE, PSI, SPEAR (Armitage et al, 1983 ; Beketov et al, 2009 ; Extence et al, 1999 , 2013 : for details of all biological indices see Table S1 ), but latterly statistical approaches have been used in conjunction with empirical data to improve these indices (MCI, WHPT, ePSI; Clapcott et al, 2017 ; Paisley et al, 2014 ; Turley et al, 2016 ; Turley et al, 2015 ) and to develop new indices a priori (Sed‐MCI, AWIC, CoFSI, BSTI, TRPI; Clapcott et al, 2017 ; Everall et al, 2019 ; Hubler et al, 2016 ; Murphy et al, 2013 ; Murphy et al, 2015 ). Now indices are available for a wide range of pressures, including among others, organic pollution, eutrophication, acidification, pesticides, excess fine sediment and flow pressures, as well as general degradation (Birk et al, 2012 ).…”