Mathematical Miracles

As every NSW school student and parent knows, the Higher School Certificate is a relative ranking, with 80 meaning that you beat 80% of your cohort. Each year’s students are compared to their peers.It doesn’t take a 4 unit maths student, therefore, to puzzle at the claim in today’s SMH that "HSC’s best are getting even better". Since we compare every year’s students against one another*, how could this be possible?

The answer turns on the meaning of "best", which is apparently defined by the SMH to mean the share of students scoring above 90% in one or more courses. In other words, the cross-course grade correlation has fallen. This might be good, or it might be bad – but I’m not sure I’d categorically class it as "getting better". Of course, the flipside is most likely that the share of students scoring below 50% on one or more courses has also risen.

* In fact, the average UAI has probably fallen a bit, since the UAI is your rank not only among test-takers, but among the age cohort. So the average UAI actually given is slightly above 50, but as year 12 completion rises to 100%, the average UAI will fall to precisely 50.

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4 Responses to Mathematical Miracles

  1. Bruce Bradbury says:

    I think the UAI is a relative rank, but the HSC marks in each subject are not. I think they are supposedly based on ‘absolute standards’ (though most students and parents consider them to be pretty meaningless).

  2. Andrew Leigh says:

    Bruce, I’m not sure that’s right (at least when I went through in 1990 it wasn’t). My understanding was that all courses were initially standardised to a mean of 50 and a SD of 10, and then rescaled so that their means and SDs were equal to the average mark of course-takers in all their other subjects.

  3. Steve Edney says:

    Andrew, I think that is right from what I remember from around then (91 for me). However they spent a lot of time trying to tweak the scaling system because people doing 4 unit maths mostly ended up with marks of 90+.

    From what this page says however it appears to be different now.

  4. Naomi says:

    They have changed from rankings to absolute marks. The change came in 2001, I was of the last ranked batch in 2000. After having the olympics in our HSC year they decided that trialing the new system on us too was a bit much.

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