“…The current state of supervision research can be compared to psychotherapy research in the 1950s or 1960s: measurement and effectiveness issues loom large as major concerns (Milne et al, ). It remains the case that ‘…although our knowledge and understanding of supervision has bourgeoned…, that which we do not understand or understand well continues to be vast’ (Inman et al, , p. 86). Hampering that understanding, supervision research has often been, and continues to be, criticised for the following reasons: small sample sizes, over‐reliance on self‐report measures, limited number of valid supervision measures, ex post facto designs, limited attention to client outcomes and lack of longitudinal data (Ellis, D’Iuso, & Ladany, ; Ellis & Ladany, ; Hill & Knox, ; Russell, Crimmings, & Lent, ).…”