UAC scaling? (1 Viewer)

[sneeble]

Hey... My bro put me onto this site, I'm just starting 12 now, will graduate next year. He just finished repeating year 12.

After about 2 months of explaining and yelling from my bro, and reading the stuff here I understand how HSC marks are calculated! Thanks to cyph, Laz, etc for all the complicated materials around here

I have a question about UAC scaling.

As I understand it to scale a subject (we'll call it X), the UAC do the following;

A scaled mean is calculated. It is the average of all the people who do the subjects average marks (their average marks being the average mark they got for the 10 units they do). So if only 3 people did subject X in one year, and their average marks across all subjects were 27/50, 35/50, 40/50 (on a 1 unit basis) the scaled mean for subject X would be 34.

Correct so far? If not, show me the light!

Now, my question - how is the scaled mean applied to peoples marks? Do they add your mark in a unit (for example 40/50) to the scaled mean (say 30/50) and average them to get 35/50 as the mark that goes to the UAI aggregate? And, is it applied to Aligned HSC marks or raw HSC marks?

I hope this made sense.

 

[Lazarus]

Originally posted by sneeble
A scaled mean is calculated. It is the average of all the people who do the subjects average marks (their average marks being the average mark they got for the 10 units they do). So if only 3 people did subject X in one year, and their average marks across all subjects were 27/50, 35/50, 40/50 (on a 1 unit basis) the scaled mean for subject X would be 34.

Correct so far? If not, show me the light!

It's actually a lot more complicated than that. The scaled mean for a course is the average of the scaled marks for that course - but the scaled mean is calculated before any marks are scaled. Sound confusing?

The scaled means for all courses are calculated at once by solving a particularly large set of simultaneous equations. In essence, the algorithm calculates what the scaling for each course needs to be to compensate for candidature difficulties, whilst preserving the relative differences between students. I would strongly suggest that (unless you have a morbid interest in these things like me) you don't worry about how scaled means are actually calculated. The mathematics involved is fairly complex, involving all sorts of weird and wonderful things like inverting matrices and calculating eigenvectors, which I didn't begin to cover until first-year uni maths. But the example you described is a useful analogy.

Originally posted by sneeble
Now, my question - how is the scaled mean applied to peoples marks?

In addition to the scaled mean, a scaled standard deviation is also calculated (according to the average of the candidatures' average spread of raw HSC marks - similar to the scaled mean).

Now, the transformation. First, remember that before any scaling processes occur, distributions of raw marks are standardised to have a common top mark, a mean of 25 and a standard deviation of 12 (on a 1-unit basis). Once scaled means and scaled SDs have been calculated, each distribution of raw marks is transformed to the appropriate scaled distribution.

To transform the mean and SD of a given distribution -
1. Subtract the original mean.
2. Divide by the original SD.
3. Multiply by the target SD.
4. Add the target mean.

This is a simple linear transformation. The one used by the Technical Committee is slightly more complex (it is a non-linear transformation, which has the added advantage of ensuring the top mark does not float above 50). But the linear transformation provides a useful analogy.

Originally posted by sneeble
And, is it applied to Aligned HSC marks or raw HSC marks?

The Board severely skews distributions of marks during the aligning process, and thus the Technical Committee resolved to always use raw marks instead.

 

[sneeble]

:jaw:

Originally posted by Lazarus
Sound confusing?

Did you really need to ask that, or was it just for effect?

Anyway, sheeeeeeeeeee-iet is about all that went through my mind the first time I read that post, but I'm pretty sure after a couple of re-reads I've got my grips on it.

I don't think I'll take up your "morbid interest" in the technicalities (gives a new meaning to the word!) of UAC scaling...

I'm content with my knowledge of how marks are screwed with... Now I've just got to get them!

Cheers Laz!

 

[Lazarus]

Just for effect.

 

[freaking_out]

Originally posted by Lazarus
...
The Board severely skews distributions of marks during the aligning process, and thus the Technical Committee resolved to always use raw marks instead.

lol i just read the last sentence...so ur saying the uac ppl, get ya mark out of 120 instead of 100 for 4u maths?

 

[Lazarus]

Yes, but the marks are all standardised first anyway. In terms of scaling, your actual raw mark doesn't really mean anything; what is important is your rank and the relative differences between students (in all courses).

Sound familiar?

 

[freaking_out]

Originally posted by Lazarus

...Sound familiar?

yeah, when u were explaining to us abt. moderated assessment marks, and how ya rank and relative diff. in ya skool, is only what matters....and now your saying that ya rank in the state matters.

can u tell me breifly what "standardised" means?

 

[sugaryblue]

Originally posted by Lazarus
Just for effect.

Ah!

Lazarus, how long have you been interested in scaling and stuff??

 

[freaking_out]

Originally posted by sugaryblue
Ah!

Lazarus, how long have you been interested in scaling and stuff??

well from what i know, he started in 2001 when he was doing his hsc....and ever since he hasn't stopped calculating uai's and talking about scaling.

 

[sugaryblue]

Originally posted by freaking_out
well from what i know, he started in 2001 when he was doing his hsc....and ever since he hasn't stopped calculating uai's and talking about scaling.

hehe... i realise that i have a newfound obsession: UAI and scaling.

 

[freaking_out]

Originally posted by sugaryblue
hehe... i realise that i have a newfound obsession: UAI and scaling.

well don't we all.

 

[Ragerunner]

Yes, sooo sexy

You'd be surprised how much you can learn from the BOS and UAC website.

I got all my information from there + Laz.

Oh well, I manage to stump Laz with a question he didn't know. *feels proud*

 

[sugaryblue]

Originally posted by Ragerunner


Oh well, I manage to stump Laz with a question he didn't know. *feels proud*

I am surprised! A question that Laz doesn't know? what was it?

 

[Ragerunner]

If you suceed in a misadventure appeal in paper 1 of English, but do the exam normally in paper 2, what would happen?

Considering your assessment mark will become your exam mark or whichever is higher, it's hard to apply that when you got 2 separate English exams, and it displays only the English you are doing in the Record of achievement. i.e. they don't show what you got for AOS or paper2, but instead both combined.

 

[Lazarus]

Originally posted by freaking_out
can u tell me breifly what "standardised" means?

The distribution of raw marks in each course is set to have a common mean of 25 and a common standard deviation of 12 - this process is called standardisation.

Originally posted by sugaryblue
Lazarus, how long have you been interested in scaling and stuff??

I accelerated computing studies in 2000, so since then.

Originally posted by Ragerunner
If you suceed in a misadventure appeal in paper 1 of English, but do the exam normally in paper 2, what would happen?

I'm thinking that there are two possible courses of action they could take:

1) Only your Paper 2 mark is used (so its weighting changes from 60% to 100%).

2) You're assigned an 'estimated' Paper 1 mark. This would be done by looking at your position in the distribution of marks for Paper 2 and then inserting you into the distribution of marks for Paper 1 at the same point.

I think the second option would be the most fair.