Monthly Archives: August 2011

Year 10 subject selection

If you're in year 10 this year, soon you'll need to choose your subjects for year 11 and 12. This decision should not be taken lightly, as your choices now will determine what you will be doing for your HSC, and by extension, have an impact on your ATAR. In this article, we will be answering the most commonly asked questions: ‘which subjects should I choose?’ and ‘how should HSC scaling affect my subject choices?’

Which subjects should I choose?

If your goal for the next two years is to maximise your ATAR, our advice to you is: choose the subjects you think you'll be good at among the subjects that offer decent scaling. Now as with most things in life, there are exceptions to this statement which we'll cover later. But before we continue, let's have a quick look at how HSC scaling works.

A crash course on HSC scaling

The way scaling works is raw exam marks at the end of year 12 are converted into scaled marks. This is to allow a direct comparison between graduates doing different subjects – sort of like swapping all of the world's currencies to a single currency so values can be compared.

Scaled marks are different to your HSC marks (actually they have nothing to do with each other, other than both being derived from your raw marks). In a nutshell, scaled marks are what determines your ATAR, so if your sole goal is to maximise your ATAR and get into the university course you want, maximising your scaled marks should be your goal for the HSC. At the end of year 12, a graduate does not see what scaled marks he or she scored, only HSC marks are shown. However their ATAR is calculated based on their scaled marks, that's why scaled marks are what's important.

How well a subject scales determines whether your raw exam marks will be pushed up or down, and by how much, when being converted into scaled marks. Doing subjects with low scaling will mean you'll need to score higher marks and higher percentiles to obtain the same scaled marks as doing subjects with higher scaling. To find out how well different subjects scale, we need to look at Table A3.

Table A3

The latest Table A3 (as at time of writing this article) is here

Table A3, entitled "Descriptive statistics and selected percentiles for HSC marks and scaled marks by course" is a set of statistics published by the UAC each year, after their Report on Scaling is published. The latest Table A3 (as at time of writing this article) is here – just Google ‘table A3' for the latest one.

Table A3 shows the HSC and scaled marks for each subject at various percentile levels, as well as the means (averages). The figure to pay attention to is the scaled mean for each subject. The scaled mean is the average scaled marks achieved per unit among the candidature of that subject for that year. For example, HSC Biology had a scaled mean of 26.9 in 2010, this means the average Biology student graduated with 26.9/50 scaled marks per unit, or 53.8/100 for the subject. The scaled mean is also an indicator of how high the subject scales, and whether it ‘scales up’ or ‘scales down’ in common schoolyard parlance.

The average scaled mean is 25 (due to the standardisation method used to convert raw marks into scaled marks). Therefore, it can be said that subjects with a scaled mean of > 25 have ‘above-average scaling’. So back to our example, Biology with a scaled mean of 26.9 scales slightly better than the average subject. Generally anything with a scaled mean beyond 30 is a good and safe choice. Some of the more common subjects that meet this criterion are:

  • English Advanced (32.5)
  • English Extension 1 (36.4)
  • English Extension 2 (36.3)
  • Mathematics (30.7)
  • Mathematics Extension 1 (39.8)
  • Mathematics Extension 2 (43.8)
  • Physics (30.5)
  • Chemistry (31.7)
  • Economics (31.0)

Now having said all that, remember we said you should choose the subjects you would be good at amongst the subjects the subjects that scale well. You'll be worse off if you chose a subject purely for its scaling, although you're terrible at it

Relative difficulty in achieving the same scaled marks

Table A3 also tells us something interesting. If you look at the scaled marks achieved for each percentile, and compare these across 2 or more subjects, you can get a picture of the relative difficulty in achieving the same result.

For example, say you're considering 2 subjects, and must choose one or the other but not both. Say the subjects are Chemistry and Senior Science.

Course Number Type of mark Mean SD Max. mark P99 P90 P75 P50 P25
Chemistry 10 330 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
Senior Science 4 901 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

If you achieved the 90th percentile in Senior Science (meaning out of 100 randomly selected students, you beat 90), you would obtain 32.8/50 scaled marks. You would have obtained more scaled marks if you achieved the 25th percentile in Chemistry instead (34/50). So ask yourself, is it easier to beat 90 out of 100 students in Senior Science, or 25 out of 100 students in Chemistry? Of course, the difference in scaling between these two subjects highlights that Chemistry has a higher quality candidature than Senior Science, but the difference between 90th and 25th percentile is big enough to more than compensate for the fact that you're up against a higher quality candidature in Chemistry than in Senior Science.

Lets look at another example. Say you're considering between Agriculture and Mathematics (2 unit) Here are the Table A3 stats for both:

Course Number Type of mark Mean SD Max. mark P99 P90 P75 P50 P25
Agriculture 1 413 HSC 35.2 7.3 49.0 48.0 44.5 40.5 35.0 31.0
scaled 20.6 11.3 47.4 45.1 36.9 29.1 19.0 11.6
Mathematics 17 152 HSC 38.2 7.5 50.0 48.5 46.0 43.5 39.5 35.0
scaled 30.7 9.4 50.0 46.5 41.9 37.9 37.9 24.8

From the table, if you achieved the 90th percentile for Agriculture, this wouldn't even give you as much scaled marks as if you achieved the 75th percentile in Mathematics. Now the difference here isn't as remarkable as the previous example, but it still highlights the point – do you feel 90th percentile in Agriculture is easier or 75th percentile in Mathematics is easier?

Not to mention Agriculture's scaling stats are probably skewed positively by selective schools like James Ruse, Hurlstone etc that like to accelerate their year 11s to finish their HSC Agriculture each year – if you take the achievements of these schools away, the true scaled mean is probably much lower.

Let's look at one more example, this time say you're wondering whether you should choose Maths Extension 1 (with intention to do Extension 2 in year 12) or stick with Mathematics (2 unit).

Course Number Type of mark Mean SD Max. mark P99 P90 P75 P50 P25
Mathematics Extension 1 9 116 HSC 40.6 7.0 50.0 49.5 48.0 46.0 42.0 37.0
scaled 39.8 6.9 50.0 49.1 47.1 44.8 41.3 36.6
Mathematics Extension 2 3 469 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
Mathematics 17 152 HSC 38.2 7.5 50.0 48.5 46.0 43.5 39.5 35.0
scaled 30.7 9.4 50.0 46.5 41.9 37.9 31.9 24.8

The first thing that might jump at you is the super-high scaled mean for Maths Extension 2 – indeed Maths Extension 2 is the highest scaled HSC subject (out of all the commonly available ones, excluding certain language subjects). If you did Maths Extension 2, even achieving in the 25th percentile would mean you score more scaled marks than someone achieving the 90th percentile for Mathematics (2 unit). Think about that for a second! It's more beneficial to your ATAR to achieve only the 25th percentile in Extension 2 than it is to achieve the 90th percentile in Mathematics (2 unit)!

One more thing – if you do Extension 2, your Maths Extension 1 counts for 2 units instead of 1 – so the marginal positive effect of taking Extension 2 to your ATAR is even greater because Extension 1's scaling is so high as well (excluding certain language subjects, Extension 1 is the second highest scaling subject). That's why most 99+ ATAR scorers have done Maths Extension 2 – it's simply the ‘easiest’ way to score a 99+ ATAR. This, combined with Extension 2's extremely high scaled mean, is why we advise all our students to take it up if they are capable at maths.

Common misconception: lots of students seem to think if they do a hard subject like Maths Extension 2, if they do poorly they may actually be ‘scaled down’; instead of up.

This is incorrect as you can see from the table above. Scaling only occurs in one direction regardless of what percentile you achieve. For Maths Extension 2, you'll get pushed up even if you only achieve the 25th percentile, which results in a 42.3/50. A 42.3 is easily a mid-high band 6 in most other subjects, but maybe a band E2 for Maths Extension 2. My point is even if you do relatively poorly in a hard subject, you still get the benefit of its high scaling.

When should I ignore scaling in choosing a subject?

The only time you should not pay attention to the scaling statistics of your subjects is if you know you can do so well in a subject that, despite its low scaling, the scaled marks you achieve will be greater than what you could have achieved in an alternative subject. Or in summary, only ignore scaling if you're extremely good at a particular subject. It's difficult to tell whether you'll be really good at something before actually starting year 11, so our advice is to ask teachers and past students to get an idea of what sort of skills are needed to succeed in a particular subject.

For example, suppose you're considering between Food Tech and Physics:

Course Number Type of mark Mean SD Max. mark P99 P90 P75 P50 P25
Food Technology 3 500 HSC 35.4 7.2 49.0 47.0 44.0 41.0 36.5 31.0
scaled 20.2 10.7 46.0 42.6 35.2 28.6 19.5 11.5
Physics 9 359 HSC 37.6 5.7 49.5 47.0 44.5 42.0 38.0 34.0
scaled 30.5 9.2 50.0 45.6 41.4 37.6 31.9 24.7

Physics is the safe choice, but suppose you're really passionate about Food Tech. You need to be confident that you can achieve, say, the 90th percentile in Food Tech as opposed to around 65th percentile in Physics (to achieve the same scaled marks). There's quite a gap in percentile for the same amount of scaled marks, but if you're confident you'll be really good at Food Tech, then go for it.



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