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3.2.6 Mark-to-grade conversion ("grade conversion") and grade adjustment

This section does not relate to the conversion of grades from Study Abroad Programmes.

Two processes are recognized: grade conversion (the movement of marks from another scale onto the 20-point scale); and grade adjustment (the re-scaling of grades).

Any conversion procedure must be reliable and transparent; should be approved by External Examiners; and should be published in advance of use.

If marking is accurate and any required conversion process is clear, grade adjustment will rarely be needed. When it is, a clear case for doing so and an appropriate methodology must be presented to External Examiners prior to the reporting of grades to the Deans. Wherever possible students should be aware of the procedures used to adjust grades.

Where a module has more than one element (examination and continuous assessment components for example) not marked directly on the 20-point Common Reporting Scale, consideration must be given as to whether any conversion should occur before or after collation. If the same conversion process (marks to grades) is used for all elements then conversion to the 20-point Common Reporting Scale can occur after the marks have been collated. On the other hand, if different conversion processes (marks to grades) are used for different elements each element must be converted to the 20-point Common Reporting Scale individually and the different grades collated to one overall grade for the module. This might be the case when, for example, it has been determined that one type of assessment out of several in the module requires a relatively high percentage score in order to pass because of critical competency issues. Note that some care must be taken in defining what an "element of a composite grade" is. An examination paper for example will typically contain several questions. It is not necessary to convert the mark for every question onto the 20-point scale: the examination is "the element". Continuous assessment might consist of one or two substantial pieces of work (essays or laboratory reports for example) but in other instances continuous assessment might be several small pieces of work that could meaningfully be aggregated before conversion. In order to maintain coherence across Schools, the Dean of the relevant Faculty should be consulted.

Grades forming part of the formal assessment of a module that are returned to students before completion of the module serve a valuable feedback and formative function. However, students must be told that all such grades are provisional until approved, first by External Examiners and finally by Deans. Grade conversion

Grade conversion refers to the procedures used in translating marks realized on a dedicated marking scale onto the 20-point Common Reporting Scale. Schools have discretion in making such conversions, but any conversion procedure must be reliable, valid and transparent and must be approved by External Examiners and the Dean of the Faculty in advance to ensure both suitability for the discipline and concordance with University practices. Grade conversion tables and/or procedures must be published to students in advance of use. There are essentially two ways of achieving grade conversion:

  • By using conversion tables set a priori that equate the marking scale used with the 20-point Common Reporting Scale. Such conversion tables must establish a clear and systematic relationship between the marking and reporting scales; the relationship need not be linear. ([1] This approach could be used, for example, when marking is done using a percentage scale, or when marking a multiple choice questionnaire – fixed proportions of marks can be equated to the 20-point Common Reporting Scale).

  • By using a post-hoc procedure that establishes benchmarks set either by student performance or by procedures that use Boards of Examiners to establish expected levels of achievement (such as the Angoff method used in the Bute Medical School). It will be possible to explain to students the methodologies in advance of use.

[1] The question of linearity is not serious if we assume that the conversion from percentage marks is approximately linear through the bulk of the grades (7–16) and that it accelerates below 7 towards zero, and over 16 towards 20. All this does is offer advantage at the top of the distribution and disadvantage at the bottom. Grade adjustment

Grade adjustment is a procedure that can be adopted (after conversion to the 20-point Reporting Scale has been completed) by a Module Board. It refers to the systematic adjustment of the distribution of grades in the module: it is neither a licence to manipulate the grades awarded to specific individual students nor to generate an artificial inflation (or deflation) of grades. Rather it is a procedure used to address anomalies in the distributions of grades for a specific question or overall grades for a module which create outcomes that might be inappropriate. For example, if three out of four elements on a module produce identical distributions of grades but the fourth has a skewed distribution that depresses the overall grade, it would be advisable to question that element. If (and only if) it could be shown that the assessment was flawed in some way, it would be appropriate to adjust the grades for that element.

It is important that the setting of assessments should be well thought out, and that all marking should be transparent, reliable, valid and as objective as possible. The intention is to mark accurately and fairly in a manner that can be reproduced by an independent marker, and can be clearly understood by students. If this is achieved it will rarely, if ever, be necessary to adjust grade distributions.

Nevertheless, there are circumstances in which it might be necessary to adjust grades, either for the overall module grade, or the grades awarded for a particular element of a module's assessment (for example, a continuous assessment exercise). Any manipulation of grades must be equitable and transparent. Students and External Examiners should understand – in advance of the fact whenever possible – under what circumstances manipulation of grades would be appropriate and what methods would be used. The following is intended as a guide to Module Boards as to when grade adjustment might be considered; note that the Deans, when signing off reported module results, will also follow this guidance. 

Grade adjustment might be thought appropriate where:-

  • Fewer than 5% or more than 30% of students have obtained a grade of 16.5 or more.
  • The highest grade(s) awarded are less than 16.9.
  • There is very strong bunching such that 80% or more of grades lie between 14–16, with few below or above this range.
  • The mean or median grade is less than 12 (for Honours modules only). 

Careful analysis of the module data might reveal specific problems with particular elements, which could be adjusted and then re-entered into the overall calculation. Alternatively, the overall grade distribution might require attention.

The following are three different forms of grade adjustment that might require intervention to ameliorate an anomalous distribution:-

  • Stretching the range (either at the top end or the bottom end, or both). This can be done using simple arithmetic by, for example, fixing a point in the grade distribution and then incrementally adding to the grades above or below, as required.

  • Compressing the range (either at the top end or the bottom end, or both). This can be done using simple arithmetic by, for example, fixing a point in the grade distribution and then incrementally subtracting from the grades above or below, as required.

  • Various mathematical transformations will change the shape of a distribution. If the results set has an unexpected distribution (bimodal for example), linear (Euclidean) transformation can be used to stretch and shift. This might be used when the range of marks is too restricted or extended (in one or other direction, or both). Cubic or quadratic transformations will have other effects on smoothing unexpectedly crazy distributions.

If Module Boards inspect grade distributions and find them to be aberrant, but have limited confidence in their ability to deal with them effectively, they should feel free to contact colleagues in other Schools who will be able to help. The Deans will give advice on whom to contact.


Nicola Milton, Executive Officer to the Proctor

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