skip to content

Natural Sciences Tripos


Marking and Classing - pre-2023

The following marking scheme has been approved by the Committee of Management for the Natural Sciences Tripos.


Examiners are nominated by the various Faculties and Departments who contribute to teaching on the Tripos and are formally appointed by the General Board. In each subject, there is a Senior Examiner and other appointed Examiners and Assessors who are responsible for setting the papers and marking the scripts. There is also a Chair of Examiners who, along with the Senior Examiners, assigns classes to candidates and produces the class list and final markbook.

Marks from individual subjects

In each subject, the Examiners produce a mark out of 100 for each candidate.

For many subjects, the final mark will consist of a component from written papers and a component from continually assessed work or written practical examination. The marks for these two components are also submitted separately; they should add up to the total mark and it should be made clear how marks out of 100 are allocated to each component.

All individual subjects devise their marking schemes so that the proportion of NST candidates in the various classes is roughly correct.  However, if it is not possible to get the desired distribution in this way marks may be scaled using a linear piecewise scaling algorithm.

Marks for each subject are norm-referenced for candidates sitting that subject. The marks are scaled such that:

  • 25% of candidates achieve a mark of 70.0-100.0
  • 65% of candidates achieve a mark of 50.0-69.9
  • 10% of candidates achieve a mark of 0-49.9

A fail is thought of as 40.0 marks and below; note, however, that in Part IA of the NST a failure in a single subject is of no particular consequence other than the low mark.

Experience indicates that large subjects (those with, say, more than 150 candidates) should have no difficulty reaching these targets to within a few percent. Smaller subjects are not expected to hit these targets so closely.

Examiners should use their discretion over the 10% target for the bottom section of the ranking category. Experience is that the numbers who can reasonably be placed in this band do tend to vary very much from year to year, even in large subjects.

If a Senior Examiner feels that there are compelling reasons to deviate from these targets they must discuss this with the Chairman of Examiners well in advance of the final meeting.

Submitting marks

The final (aggregate) mark will be shown rounded to one decimal place in the final markbook, but as there may be intermediate stages of manipulation it is required that marks from individual subjects be submitted without any rounding.

Classing procedure

For each subject all candidates are placed in a rank order, based on the total mark out of 100.  In drawing up the rank order, candidates who have missed all components of the examination for that subject are omitted: likewise, candidates from other triposes are omitted.  Candidates are assigned a percentile rank based on this rank order, with a percentile rank of 100 being given for the highest mark and 1 for the lowest.  For each candidate, the three percentile ranks are summed (with a weighting of 0.75 for Mathematics and Mathematical Biology) and divided by 3.75 to produce a mean percentile rank for the Tripos (out of 100).  Candidates will then be ranked according to this mean percentile rank and the Senior Examiners will use this ranking to assign a class for the Tripos.  These classes will be assigned such that:

  • 25% of candidates for the Tripos achieve a 1st class
  • 67.5% of candidates for the Tripos achieve a 2nd class
  • 7.5% of candidates for the Tripos achieve a 3rd class or fail.

Small deviations from these percentages may be justified (especially in the 3rd class and fail categories) depending on the field of candidates.

In addition to the mean percentile rank, an aggregate mark will also be calculated for each candidate by summing the four subject totals out of 100 (with a weighting of 0.75 for Mathematics and Mathematical Biology).  Candidates who achieve 149 or less marks out of the maximum 375 will not necessarily be awarded honours, although this will be a decision of the Examiners.

The final boundary marks used and the number of candidates in each class are included in the final markbook which is sent to Colleges.

Note: Because a candidate's class is based on their mean percentile ranking rather than their aggregate mark, there will be a few instances where candidate A has a higher aggregate mark than candidate B but a lower class. The Final Markbook that is distributed to Colleges after the Final Examiners Meeting will have the percentile rankings in each subject and the overall mean percentile ranking, which is what is used to decide each candidate's class.