Monthly Archives: February 2011

Can I Score a High Atar With Low Scaling Subjects?

Can I Score a High Atar With Low Scaling Subjects?

A commonly pondered question by many students is whether their subject choices made at the end of year 10 would preclude them from getting a ‘high ATAR’. Now, what does ‘high ATAR’ mean to you? What constitutes a high ATAR to one person will differ to the next as it is a subjective question relative to one’s ability and expectation, amongst other things. For argument sake, let us suppose that a ‘high ATAR’ is anything above 99 (understandably this may be more appropriately deemed a ‘very high ATAR’ to some). Now therefore the question becomes ‘can I still get 99+ with relatively low scaling subjects?”

The short answer is: yes, of course you can!*

*The long answer:

You may already have at least a vague idea of how the HSC scaling process works, so you may be able to understand that there is theoretically some trade-off between how well a subject scales, and how difficult it is (if there was such a thing as an objective measure of subject difficulty). What this implies is that if your HSC portfolio is mostly low scaling subjects, your level of achievement within each subject would have to be comparatively higher than if your portfolio consisted of mostly higher scaling subjects. What this may mean generally is that 10 units worth of 90s (HSC aligned marks) in low scaling subjects may result in the same ATAR as 10 units worth of 80s in higher scaling subjects.

Let’s look at some hard numbers to support our thesis. Each year, the UAC publishes a set of scaling statistics in Table A3, as part of each year’s annual Scaling Report. The latest years of table A3’s are available on the UAC website, or at: Table A3 compares all available HSC subjects in terms of several statistics, the important ones being: the scaled mean and the mean HSC mark. The scaled mean represents the average scaled mark achieved among the entire candidature of the subject, while the HSC mark mean represents the same for HSC mark. On this note, the Table A3 statistics are what’s used as inputs in ATAR calculators you will find around the web.

Now let’s look at some examples

Example 1

Suppose one student did Chemistry and another student did Senior science. If the Chemistry student scored in the 90th percentile in the 2010 HSC, their HSC mark would be 90 and his scaled marks would be 84.4. The Senior science student would need to achieve a HSC mark of 97 (estimate based on interpolation) and come close to being 1st in the state in order to earn the same number of scaled marks! (Remember, your ATAR is directly calculated off the total of your scaled marks across your 10 best units – it is scaled marks that gets you into the Uni course you want!)

Courses Number Type of Mark Mean SD Max Mark P99 P90 P75 P50 P25
General Mathematics 30992 HSC 35.8 5.9 50.0 47.0 43.5 40.0 36.0 32.0
Scaled 21.1 10.0 45.4 41.0 35.0 29.1 20.8 12.9
Mathematics Extension 2 3469 HSC 41.8 5.4 50.0 48.5 47.0 46.0 43.0 39.0
Scaled 43.8 4.5 50.0 49.2 47.9 46.6 44.8 42.3

Example 2

Lets look at another set of contrasting subjects, to reinforce the point being made. Suppose one student does General Mathematics and another student does Maths Extension 2 (unfair comparison yes, but relevant in illustrating the point at hand). If the Maths Extension 2 student scored in the 90th percentile, their HSC mark would be 94 scaled mark would be 95.8. For the general mathematics student, even if he/she topped the state, only 90.8 scaled marks would be awarded.

Courses Number Type of Mark Mean SD Max Mark P99 P90 P75 P50 P25
Chemistry 10330 HSC 37.4 6.5 49.0 47.0 45.0 42.0 38.0 34.0
Scaled 31.7 9.2 50.0 45.9 42.2 38.8 33.5 26.1
Social Science 4901 HSC 38.0 5.1 49.5 47.5 44.0 41.5 38.5 35.0
Scaled 19.5 9.9 43.8 40.3 32.8 27.1 19.3 11.5

In 2010 there were 3469 Maths Extension 2 students, and 30,992 general maths students – almost ten times more students than Maths Extension 2! What the scaling system does is that you are rewarded less for coming first out of 30,992 students compared to coming in the 90th percentile among 3469 students (equal to around 347th).


While the results of these examples do sound amazing, it is acceptable from a statistical / technical analysis – the system rewards students who embark on more difficult subjects like Maths Extension 2 and Chemistry. From a technical standpoint, the system is ‘fair’. For those of you aiming for a ‘high ATAR’, this means you will need to score very high percentiles across all your lower scaling subjects in order to score a 99+ ATAR. This is difficult but not impossible and certainly not unheard of. As a general guide, for all your low scaling subjects (subjects with scaled means of 25 and below) you should aim to score a HSC mark of 95 or better, in order to not jeopardise your chances of achieving the magical 99+ ATAR.

A slight digression from topic: the significance of a 99 ATAR is the fact that Law and Medicine (though based on UMAT and interview results as well, the fact that median ATAR of UNSW and USYD medicine students are 99+ means ATAR is at least a significant indicator of chances of success in gaining admission to these courses)



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