Between 1963 and 1986 A-Level grades were awarded according to norm-referenced percentile quotas (A <= 10%, B = 15%, C = 10%, D = 15%, E = 20%, O/N = 20%, F/U >= 10% of candidates). The validity of this system was questioned in the early 1980s because, rather than reflecting a standard, norm referencing might have simply maintained a specific proportion of candidates at each grade. In small cohorts this could lead to grades which only indicated a candidate's relative performance against others sitting that particular paper, and so not be comparable between cohorts (e.g., if one year, only 11 candidates were entered for A-Level English nationally, and the next year only 12, this would raise doubt whether the single A awarded in year one was equivalent to the single A awarded in year two). In 1984 the Secondary Examinations Council decided to replace the norm referencing with criteria referencing, wherein grades would be awarded on "examiner judgement". The criteria referencing scheme came into effect in June 1987, and since its introduction examiner judgment, along with the merger of the E and O/N grades and a change to a resitable modular format from June 2002, has increased the percentage of A grade awards from 10 to >25%, and the A-E awards from 70 to >98%.