Tag: HSC Scaling

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: http://www.duxcollege.com.au/hsc-scaling-statistics-i-34.html. 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)

Is the HSC a Game?

You may have heard people call the HSC a game, or liken it to a game. Well there is an element of truth to this view, depending on how you look at it.

In order for the HSC to be fair in ranking students for the purposes of University entry, a comprehensive system of HSC scaling is used, hence why we have the UAC and the notion of ‘scaling’ and ‘scaled marks’. The scaling process itself is firmly justified mathematically, and is technically fair (to those who understand the mathematics of it – first-year statistics anyone?). This is also PART of the reason why English is a compulsory subject (because the HSC scaling process relies on having a common subject taken by all HSC students as a sort of ‘parametric variable’ to enable comparison).

Now, without going into how scaling works (read our HSC scaling explanation for more info), it’s a given that this scaling system has a HUGE effect on your final result – your ATAR. Obviously choosing subjects that have scaled well in the past would have a big positive impact on your ATAR, simply because of the effect of scaling. Of course, these subjects scale high because they are comparatively ‘harder’ to get higher marks in, according to the scaling system. But the problems with advising people to choose higher scaling subjects are:

  1. If you don’t enjoy the subject, you may get a low mark anyway. No amount of scaling can save a disinterested and unmotivated student from getting a low mark in a particular subject.
  2. Choosing subjects for their scaling will not prepare you for the University course you may end up with.

But perhaps the biggest problem of all is the fact that the all-important subject selection decisions are made at the end of year 10. Effectively, the effect of HSC scaling would already be set in stone before you even started year 11! So why advise year 11s and 12s about HSC subject scaling at all when they aren’t able to change their subjects by then anyway? (with the exception of taking up Extension 2 maths). So in this respect, yes the HSC is like a game, because if you understand the rules of scaling, you can use it to your advantage in choosing your subjects wisely at the end of year 10.

Therefore, YES it is an EXCELLENT idea, if you are in years 7-10, to familiarise yourself (at least on a basic level) of how HSC scaling works, and how this should affect your subject selection decisions (if at all). However, if you’re already in year 11 and 12, this is not an option for you.

Nevertheless, year 11s and 12s that have already chosen their subjects for the Preliminary and HSC course should note that there’s actually one more important benefit of knowledge about HSC scaling.

The efficient allocation of study time

The main benefit of knowing how HSC scaling works, is to use it to plan your study schedule effectively. The reason is since some subjects are more highly scaled than others, some subjects have different rates of diminishing returns than others. Put in another way, some subjects are worth your time more than others.

General rules

Generally, the best way to allocate effort and time to your subjects is:

  1. If your skill is about the same in all subjects, spend more time on the higher-scaled subjects
  2. If your skills are much more advanced in high-scaled subjects than in lower scaled subjects, focus slightly more in your lower-scaled subjects
  3. If your skills are much more advanced in lower-scaled subjects than in higher scaled subjects, focus MUCH more on your higher-scaled subjects

The above may appear to be ‘common sense’ to some students – and rightly so, it is not a magical formula or a breakthrough strategy in HSC study. The key to a 99+ has always been to do well in as many subjects as you can!

But to illustrate the above, consider the following simple example:

Say you’re doing as well at Chemistry, and as you are doing at Maths Extension 2, then instead of splitting your study time equally between the two (just because they are both worth 2 units each), you should spend more time on Extension 2, simply because it scales higher. The higher scaling means that your return on effort is higher in Maths than in Chemistry (basically the benefit from studying is higher in Maths than in Chemistry, in this case).

In a similar example, say you are very, very good at Maths Extension 2, and terrible at English Advance. In this case, simple logic states you should spend more time studying for English and less time on Maths (despite the fact that Maths would have a much higher scaling effect than English). The reason is because if you’re already very good at a highly scaled subject, chances are you’re going to get close to a 50/50 scaled mark per unit for your Maths subjects, whereas if you spend more effort and time into English, you may raise your English scaled mark from 40/50 to 45/50 – all in the noble cause of maximising one’s ATAR.

Diminishing returns on scaling
Looking at Table A3 statistics gives an indication as to how scaled marks taper off at higher percentiles for different subjects. Generally, higher-scaled subjects have a greater diminishing return at higher percentile achievements than lower-scaled subjects.

To illustrate what this means, compare the 2008 scaled marks for Mathematics Extension 2, and Chemistry (both are highly scaled subjects, but the former is extremely highly scaled). At the 99th, 90th and 75th percentile, the scaled mark for Mathematics Extension 2 is 49, 47.5 and 46 respectively, whereas the same for Chemistry would be 48, 45.5, and 42 respectively. This shows that, assuming raising your percentile rank from 75th to 99th percentile is of similar effort across subjects, it is far more worth your time spending it on Chemistry than it is on Mathematics Extension 2. If you raised your percentile from 75th to 99th in Chemistry, you would have gained 6 scaled marks per unit, instead of 3 scaled marks per unit for Maths Extension 2.

The best way to understand exactly how to optimise your study time allocation, it’s best to have a close look at the most recent Table A3 statistics for your subjects. Look at how many scaled marks you’ll gain as a result of equal leaps in percentile ranks, and decide how to best allocate your study time from that analysis.

So to answer the original premise – yes the HSC is like a game. It has a set of rigid rules, and those that understand the rules can use it to their advantage. However, as we discussed, the advantage to year 11s and 12s is only in allowing you to better allocate your time and effort across your subjects. No amount of scaling will save you if you simply do badly in your assessments and exams.
To get a 99+, there’s still no substitute for hard work.

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