Top Marks Outperforms Experienced Human Markers: Edexcel IGCSE English

A recurring question we’re asked: how accurate are your English GCSE marking tools?

So we decided to conduct an experiment.

On their website, Edexcel publish exemplar answers for their English IGCSE. For the 40-mark Modern Prose question, there are a fairly large number of such essays on offer. These essays are made available for standardisation purposes - so teachers can see what various levels of responses actually look like in the wild.

We downloaded 50 of these essays – all handwritten – and put them through our Modern Prose marking tool. Then we measured the correlation between the official marks the board gave the essay, and the marks Top Marks AI gave those essays.

We used a measurement called the Pearson correlation coefficient. In short:

• • A value of 1 would mean perfect correlation -- when one marker gives a high score, the other always does too, and when one gives a low score, the other always does too.
• • A value of 0 means no correlation whatsoever -- knowing one marker's score tells you nothing about what the other marker gave.
• • Negative values would mean the markers systematically disagree - when one gives high scores, the other gives low ones.

For context, how do humans perform?

What sort of correlation do experienced human markers achieve when marking essays already marked by a lead examiner?

Cambridge Assessment conducted a rigorous study to measure precisely this. 200 GCSE English scripts - which had already been marked by a chief examiner - were sent to a team of experienced human markers. These experienced markers were not told what the chief examiner had given these scripts. Nor were they shown any annotations.

The Pearson correlation coefficient between the scores these experienced examiners gave and the chief examiner was just below 0.7. This indicated a positive correlation, though far from perfect. If you are interested, you can find the study here.

How did Top Marks AI perform?

Top Marks, across the 50 essays, achieved a correlation of above 0.9 -- an incredibly strong positive correlation that far outperforms the experienced human markers in the Cambridge study. (Top Marks AI was also not privy to the “correct marks” or any annotations).

You can explore the detailed marks in the embedded Google Sheet below. 80% of the marks we gave were within a 10% tolerance of the mark given by the chief examiner -- another indication of the high degree of accuracy we are achieving. You can also access the 50 exemplars here, and see where we sourced them from.

Can I see a graph to help me visualise this?

Absolutely.

First, here’s a scatter graph to show you what a theoretical perfect correlation of 1 would look like:

Now, let’s look at the real-life graph, drawn from the data above.

On the horizontal axis, we have the grade given by the exam board. On the vertical, the grade given by Top Marks AI. The individual dots are the essays -- their position tells us both the mark given by the exam board and by Top Marks AI. You can see how closely it resembles the theoretical graph depicting perfect correlation.

The Handwriting Factor

As mentioned, all the essays we downloaded were handwritten. That Top Marks was able to correlate so closely with the official board grades indicates not only its marking efficacy, but also the strength of its transcription technology.

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For more information, contact us at info@topmarks.ai.