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!)

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.

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).

Conclusion

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)

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.

Conclusion
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.

Scaled mean of HSC maths of all levels for the year 2008 were HSC Maths (2 unit) – 30.4, HSC Mathematics Extension 1 – 40.0 and HSC Mathematics Extension 2 – 44.5 respectively.

Scaled mean of HSC maths of all levels for the year 2007 were HSC Maths (2 unit) – 30.5, HSC Mathematics Extension 1 – 39.6 and HSC Mathematics Extension 2 – 43.7 respectively.

The HSC mean mark of HSC maths of all levels were HSC Maths (2 unit) – 38, HSC Mathematics Extension 1 – 40 and HSC Mathematics Extension 2 – 41.8.

From these statistics, we see that all levels of maths have actually increased in scaled mean, with the exception of 2 unit maths. In particular, Maths Extension 2 has increased from a scaled mean of 43.7 to 44.5. This has placed Extension 2 as the second highest scaled subject available to students (first being Classical Greek Extension, at 45.2).

Apart from this, Scaled mean of HSC English Advanced for the year 2008 and 2007 was 31.3 and 31.2 respectively. Moreover, its HSC mean mark was 39.7. Basically, in terms of the benefit to a student’s ATAR, an average raw mark in Maths Extension 2 is equivalent to scoring in the top 2-3% for HSC Physics, Chemistry, or English Advanced. If you score the average raw mark for Maths Extension 2, the number of scaled marks added to your aggregate mark (which is used to calculate your rank position and ultimately ATAR) is the same as if you scored in the 97th-98th percentile in some other relatively high scaling subjects, like HSC Chemistry or Physics. These numbers illustrate the huge scaling effect of Extension 2 maths.

(To find out more about how the HSC scaling process works, read our comprehensive article on the HSC scaling process).

Similarly, Maths Extension 1 also benefits from a large positive scaling effect. In 2008, its scaled mean of 40.0 means that if you scored the average raw mark in Maths Extension 1, the number of marks added to your aggregate mark is the same as if you scored in the top 15% for HSC Chemistry, or Physics, or the top 10% in Biology.

How will the ATAR affect me? The ATAR is a similar (but not identical) rank-based scale used to differentiate student performance for the purpose of university admissions. Like the UAI, the ATAR is a rank-based index, meaning the same rules of HSC scaling would apply under the ATAR.

Students should remember that just like under the UAI system, it is your rank relative to other HSC students which determine what ATAR / UAI you will receive. That is, based on your aggregate mark (out of 500), your percentile position will be calculated, and this will be directly converted into an ATAR. As a result, the number will change when converting from UAI to ATAR, however your rank remains the same. As a result, university ATAR cut-offs for all courses will be converted to match the previous equivalent rank cut-off.

For example, say Bachelor of Commerce at UNSW has a UAI cut-off of 90.00. Say this translates to a rank cut-off at the 8,800th student from the top rank. The ATAR cut-off would be adjusted to match the rank, and not be converted according to some arbitrary process. E.g. according to UAC’s published UAI to ATAR conversion table, a UAI of 90 converts to an ATAR of 90.80.

Converting from UAI to ATAR score

Read UAC’s full conversion table here.

Because both the UAI and the ATAR are rank-based scores, they are directly comparable to previous years’ UAI scores. So if you have an older brother or sister and want to best them in the HSC, the implementation of the ATAR system won’t affect that! Notice that the highest attainable ATAR is 99.95 (instead of a UAI of 100). As a result, UAI’s near 100 (above 99.7) are converted to a slightly lower ATAR score, and all UAI’s lower than 99.2 are converted to a slightly higher ATAR. For the vast majority of students, this makes their university entrance score look slightly better! However, again we remind you that your rank is not affected by these changes, and therefore the difference in numbers between the ATAR and UAI make no difference to you.

Scaled marks versus HSC marks

A commonly misunderstood concept is the relationship between HSC marks and scaled marks. HSC marks are the marks the Board of Studies awards you, and appear on your Record of Achievement. These marks determine which performance band you fall in (e.g. Band 6 or E4) for each of your HSC subjects. These marks measure how well you did according to the subject’s requirements. E.g. if you received a Band 6 in English Advanced, it means your performance satisfied all the criteria required by the HSC English syllabus to achieve a Band 6. However, in any year, any amount of HSC students can get a Band 6. For example, in a particularly smart year, a higher proportion of students may receive Band 6 in English Advanced. It is not how well you do in your subject, but rather, how well you do relative to other students which determine your UAI. Here’s where your scaled marks come into play.

Your scaled marks will NOT be shown to you at the end of your HSC, as you will only be shown your HSC marks (aligned marks, to be precise). Ironically, it is your scaled marks which are the most important determinant to your UAI. Scaled marks are calculated by the UAC (not the BOS) under a totally different process. Basically, these marks measure your performance relative to other students. (For a more technically accurate discussion on scaled marks and what they mean, as well as the mathematics behind UAI calculation, please read our article on the mechanics of HSC scaling) Remember, your HSC marks are a measure of how well you did in your subject, but your scaled marks measure how well you did relative to other students. It is your scaled marks which are used to calculate your UAI, not your HSC marks.

Through the process of scaling, the UAC converts your raw examination marks (the actual marks you received in your external and moderated internal assessment) into scaled marks. These scaled marks are then added up to arrive at your aggregate mark (students refer to this as your ‘aggregate’) out of 500. The UAI is simply a percentile rank of your aggregate, which is the total of your scaled marks in your top 10 units.

How can knowledge of HSC scaling help me?

Understanding the process allows you to plan your HSC, to an extent, in such a way as to make scaling work to your advantage. For example, if you enjoy maths, you should choose Maths Extension 2 in order to take advantage of its enormous scaling effect. Similarly, if you enjoy science, you should take Chemistry and Physics, as they scale relatively well.

In other words, comparing subjects in terms of their scaling effect can assist you with your decision as to which subjects to take for your HSC. In order to quantitatively compare the scaling effect of different courses, you will need to get familiar with reading statistics published by UAC. The rest of this article will highlight the important things to note.

Reading ‘scaled means’

Firstly, what are ‘scaled means’? The scaled mean for each subject is the average scaled mark received by all students who took that subject for that year. For example, in 2008, the scaled mean for Maths Extension 2 was 43 out of 50. This means that among the Maths Extension 2 students in 2008, the average of their scaled marks was 43 out of 50. This subject has traditionally been one of the highest scaled subjects available for the HSC. In terms of reading these scaling statistics, generally the higher the scaled mean, the higher the scaling effect.

Each year, the UAC publishes a scaling report which contains important scaling statistics for all HSC subjects eligible to contribute to a UAI. For more information, read about UAC scaling statistics. In the report, there is an important section called Table A3, which is a table setting out the scaled means of all subjects.

To illustrate the effect of scaling, in 2008, a Maths Extension 2 student only needs to be in the top 46% out of all Maths Extension 2 students to get a scaled mark of 45 out of 50 (or 90/100). A Maths (2 unit) student would need to be in the top 3% out of all Maths (2 unit) students in order to achieve the same result. These facts are read off the UAC scaling report. In the 99th percentile, a Maths (2 unit) student receives a scaled mark of 46.1 out of 50. In the 75th percentile, a Maths Extension 2 student receives a scaled makr of 46.2 out of 50. Arguably it is easier to be above average in Maths Extension 2 than to be near the top of the state in Maths (2 unit). This is the main benefit derived from choosing high scaling subjects.

Effect on UAI calculation

Simply put, the higher the total of your scaled marks, the higher your UAI will be. Sometimes when students choose subjects with lower scaled means, do spectacularly in their HSC (e.g. receive Band 6 for all of their units) but receive a UAI that is lower than what they had expected.

For example, if you did English Standard, IPT, Legal Studies and Biology, and scored 90 in all of your subjects, your UAI would be around 94 in 2008. While this is in no way a poor UAI, if you received the same HSC (aligned) marks for English advanced, Maths Extension 1 & 2, Chemistry and Physics, your UAI would be in the vicinity of 99. Again this is because of the scaling effect across different subjects. While all subjects are different and some will be more difficult than others, the best approach to dealing with HSC scaling is to choose the subjects you are interested in, while giving consideration to the scaling effect of your choices. (For more information, read our article on HSC subject selection)

In fact, the rational way to allocate study time is to allocate more time to the higher-scaled subjects, as they will be more beneficial to your UAI than lower-scaled subjects. Historically English Advanced has a scaled mean of around 30, which is practically equal to the scaling of HSC Chemistry and Economics in the past several years. These trends are not expected to change significantly year to year, so we can expect the same for at least the near future. If you’re a student who does English Advanced and Maths Extension 2, you should definitely focus more of your time on your mathematics subjects, given that both Maths Extension 1 and Extension 2 counts for 2 units each. Keeping in mind that the scaled mean for Extension 1 is around 39-40 in recent years, and that of Extension 2 is around 43-44, this makes these subjects unparalleled in terms of scaling power, and definitely deserves more attention than English.

That is not to say you should neglect English either. Treat it as you would any other subject. There is nothing special about English, except for the fact that it is the only compulsory subject in the NSW HSC, because of the way scaling works and UAI is calculated, which requires a common denominator for comparison. However this mere fact does not affect the individual student. There are rumours and misinformation floating around over student forums and by word of mouth, but the simple fact of the matter is that English is just like any other subject and is given no preferential treatment when it comes to UAI calculation. Therefore if this is the case, English should not be given any special treatment by students either. What this means is you should split your time equally as you would any other subject that scales similarly (e.g. Chemistry, Economics).