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GAMSAT Scoring - The Definitive Answer



 
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Davo
Regular


Joined: 06 Jun 2006
Posts: 10
PostPosted: Wed Apr 04, 2007 9:56 am    Post subject: GAMSAT Scoring - The Definitive Answer Reply with quote
Hi everyone,

There's been a lot of posts about how the GAMSAT scores are calculated. I came across this report from the ACER people detailing the results of GAMSAT95 which you may be interested in.

(It won't let me post the URL, search for GAMSAT95 in Google)

The important section is this:

Quote:
GAMSAT SCORING PROCESS

GAMSAT scoring is based on item response theory (IRT) methodology, a widely used procedure whereby items are calibrated to provide an estimate of the difficulty of each, expressed on an interval scale in terms of logits. Candidates scores are expressed on the same interval scale as ability estimates which are then rescaled onto a GAMSAT scale in the ange 0 - 100 for each of the three sections using the linear ransformation:

GAMSAT Section score = (estimate in logits + 5) x 10

The mean and standard deviation of Section I scores are used to standardise the scores on Sections II and III. The GAMSAT Overall score is calculated as a weighted average of the three section scores using the formula:

Overall Score = (1 x Section I + 1 x Section II + 2 x Section III) / 4

Each Section II (Written Communication) task is marked by three independent raters, using a ten-point scale. Differences of 5 or more marks are considered discrepant and result in a fourth marking. The three closest marks for each piece of writing are then summed.



Hope this helps.

Paul
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p2409
Grizzled


Joined: 02 Mar 2007
Posts: 110
Location: Melbourne
PostPosted: Wed Apr 04, 2007 1:49 pm    Post subject: Reply with quote
Wow that's complicated.
See this page for a reasonable intro into what's going oin.
http://www.creative-wisdom.com/computer/sas/IRT.pdf

Seems to me that the technique adjusts for 'easy' and 'hard' questions. So, if two people got say 67 out of 110 right, the one who got more of the 'hard' questions right will get a better GAMSAT score. 'Hard' is measured by how many other people got it right.

The choice of Section 1 to set the population s.d sounds like it's done because that bit of the test DOES have a nice normal/widish distribution, whereas maybe the science section is skewed...mmm don't know.
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AyJay
Rookie


Joined: 07 Apr 2007
Posts: 3
Location: Qld
PostPosted: Sat Apr 07, 2007 6:37 pm    Post subject: Thanks for the insight! Reply with quote
Now I know I'm getting a score of 35! Sad
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