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 Post subject: Standardised scores - KentPosted: Mon Oct 22, 2012 11:31 pm

Joined: Wed May 02, 2012 4:10 pm
Posts: 49
When I read the Kent super selective threads parents talk of their children 'only' scoring an aggregate of 410 however it is my understanding that test scores are standardised so that a score of 100 would be average for the general population of year 6s (including those that don't sit an 11 plus), a score of 130 puts a child in the top 2% roughly (aggregate of 390) and a standardised score of 133-138 would put a child in the top 1% of the whole population of year 6s while a score of 139 (aggregate of 417) or above would put them in the top <1%.
http://www.nfer.ac.uk/nfer/research/ass ... scores.cfm

All of the normal distribution curves demonstrating 11 plus standardised scores show that a score of 130 or above equates to the top 2% of the population.

So if this is the case why do Kent parents talk of their children *only* scoring an aggregate of 400 - 417 (if this equates to the top 1% of the population or above). Is it because this isn't enough for super selectives in West Kent? Do the super selectives in West Kent take the top 0.7% of the whole population roughly?

Just wondering because I've only seen Kent parents post aggregate scores above approximately 410 with a few posting scores that mean their child didn't pass, and I haven't seen people posting aggregate scores between 360 and 400.

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 Post subject: Re: Standardised scores - KentPosted: Tue Oct 23, 2012 8:42 am

Joined: Thu Jun 02, 2011 9:17 pm
Posts: 299
This looks to me like 'old' information. Think about it...if the 11+ selects the top 21% of the cohort, all of which have to score above 119/120 then this analysis does not add up. These days you would see a wider spread across the upper and lower ranges of the scores and I would expect the bell curve to be less steep.

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 Post subject: Re: Standardised scores - KentPosted: Tue Oct 23, 2012 9:41 am

Joined: Wed May 02, 2012 4:10 pm
Posts: 49
I know the Kent results don't seem to fit the standard bell curve for 11 plus, IQ, Mensa tests etc with 100 being the average and about 68% of people being within 1 SD of the mean etc but I don't understand why they don't since standardised results are supposed to be fitted to the normal distribution curve with 2% getting above 130 etc.

If you look at any normal distribution curve for intelligence (mensa tests, 11 plus etc) then giftedness equates to the top 2% of the population and the standardised score given for the 2% cut off is 130.

Even if the curve is less steep surely the results are still standardised so that only 2% get above 130? It's been a very long time since I studied stats so I can hardly remember any of it but it doesn't make sense to me to change the percentiles that correlate with any given standardised score since the whole point is that standardised test results can be compared with other standardised tests whereas raw scores can't because any two papers can be of varying difficulty.

Maybe subsequent populations are scoring higher but the data that they use to standardise results against hasn't been revised - is that what you mean?

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 Post subject: Re: Standardised scores - KentPosted: Tue Oct 23, 2012 10:06 am

Joined: Thu Jun 02, 2011 9:17 pm
Posts: 299
The thing is, due to the increasingly competitive nature of 11+ tests there are more children scoring highly, which in effect is causing an increase in lower scorers. Of course there is the average in between but i think you will find that more children are scoring above and below this average causing the bell shape to flatten out slightly. I'm no expert but this makes absolute logical sense to me. And I have found that what was once a rare score 10 years ago is now more common especially in concentrated superselective areas. Hence the reason why SS's have gradually increased their cut off scores to ridiculously high amounts.

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 Post subject: Re: Standardised scores - KentPosted: Tue Oct 23, 2012 11:23 am

Joined: Thu Oct 18, 2012 3:26 pm
Posts: 14
It’s an interesting, if frustrating, exercise in statistics. I think the bell curve will remain the same with the top 2% getting over 130 in the tests. The nature of the SS’s in west Kent means that there will probably be a concentration of children there who have the higher marks because they knew they needed the higher marks.

But the difficulty of the tests varies from year to year. Last year seems to have been an exception in terms of high marks for the SS’s but the total percentage who scored the high marks, statistically, must have remained pretty constant, regardless of the difficulty of the tests. If the tests were easier then higher marks would be needed and vice versa.

Based on this, there will be less than 1% who scored over 420 ( the 421’s, 422’s and 423’s will all be in this group). If 11,800 children took the test then this means considerably less than 118 children scored above this last year. With Judd going down to 417/418 last year and Skinners down to 411 (I think), then, taking away the girls, they are either travelling there from all over the county and OOC or there was a super concentration of the high passes in the West Kent area. I suspect a combination of the two.

45% of children passed the test this year which statistically works. However we don’t yet know if we have a super concentration of high passes in the West Kent area.

Knowing that our DC’s will have guessed some of the answers, for the top marks, the difference between who scored the top marks and those below 410 might literally amount to just four or five marks over the three tests so it could just be those who were lucky with their guesses scraped through to a sufficient score for the SS’s and that might only be one or two marks!

It doesn't affect us, but there have been cases on here where the DC's scored 141, 141 and 119 for a total score of 401 but based on the 120 cut off means that they weren't deemed as suitable for grammar. How that fits into the curve I'm not quite sure.

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 Post subject: Re: Standardised scores - KentPosted: Tue Oct 23, 2012 11:28 am

Joined: Mon Oct 15, 2012 10:44 am
Posts: 115
There are clearly people on this thread more academically astute that me!

Can any of you off an opinion (be it personal)..

Do you think 417 will get into Skinners this allocation?

I was worried that the 414 of last year, plus an inevitable rise of 2 due to it increasing every year and a further rise of 2 or 3 due to 420-423 would mean we're very very borderline...

But some of your posts make me think 417 could be good?

Thanks,

xx

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 Post subject: Re: Standardised scores - KentPosted: Tue Oct 23, 2012 11:37 am

Joined: Tue Jan 01, 2008 1:05 pm
Posts: 515
Couple of factors.

1. Only about 50%, I think, of the cohort take the 11 plus, so the 11 plus takers are generally already in the upper 50% or so ability wise.

2. Possibly more relevant. The Kent results are, I understand, standardised against a national sample, the vast majority of which do not take the 11plus, or other selective tests. In contrast much of the Kent cohort has been coached and tutored to pass CAT type tests. Hence why the Kent numbers are so high.

Scores of between about 360 and 410 get little mention on the Kent forum because their are only really two categories of marks relevant in the Kent area. A pass (ie 360 and above), which is what is necessary for most GS's, and about 410 and above, for the super-selectives. (The are a few other local variations, such as MGS for part of it's intake)

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 Post subject: Re: Standardised scores - KentPosted: Tue Oct 23, 2012 11:47 am

Joined: Tue Jul 21, 2009 9:56 pm
Posts: 8208
OOC Mum, has it ever been as high as 417 for Skinners? What has it been year on year for the last ten years say? That should give you some assurance about 414. I'm not familiar with Skinners figures. I'm not sure that your two reasons for adding loads of extra points to last year's cut-off are viable ones ...... so it might not be as bad as you think but in all things "school" there seem to be no guarantees.

Do you have a plan B you are happy with?

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 Post subject: Re: Standardised scores - KentPosted: Tue Oct 23, 2012 12:06 pm

Joined: Mon Oct 15, 2012 10:44 am
Posts: 115
mystery wrote:
OOC Mum, has it ever been as high as 417 for Skinners? What has it been year on year for the last ten years say? That should give you some assurance about 414. I'm not familiar with Skinners figures. I'm not sure that your two reasons for adding loads of extra points to last year's cut-off are viable ones ...... so it might not be as bad as you think but in all things "school" there seem to be no guarantees.

Do you have a plan B you are happy with?

Plan B is wonderful, but again we are boardline for criteria, we have the required pass, but are about 0.5 mile off catchment and they are catchment driven...but each year a couple of boys get in from our village...

Oh here we go again with the waiting and hoping.....

Plan C also very good, but not grammar and no where near as good a 'fit' with DS as plans A and B

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 Post subject: Re: Standardised scores - KentPosted: Tue Oct 23, 2012 12:10 pm

Joined: Thu Oct 18, 2012 3:26 pm
Posts: 14
My personal opinion..

Do you think 417 will get into Skinners this allocation?

If I had to put widows' and orphans' money on it, yes.

I was worried that the 414 of last year, plus an inevitable rise of 2 due to it increasing every year and a further rise of 2 or 3 due to 420-423 would mean we're very very borderline...

The problem is that we are looking at the last two years and making a pattern where they may not be a pattern in the first place. Two years is not enough to make that conclusion. A few years ago a score of below 410 would get you into the SS's.

The 11+ is not like the GCSEs and A-levels which have an overall increase in top scores and decrease in lower scores.

There will be no children who will have scored 100% in the 11+ but let's say, for instance, that the tests were really easy and many more scored well into 90%+. That wouldn't mean that many more passed. It just means that the curve is shifted towards the higher marks.

I am hoping that the last two years were an exception. The 423 thing is irrelevant as it will still be the same number of children who score over 420. It just means that a little bit more differentiation is possible but this may only have been one or two more correct questions.

Our DS scored 408 with scores well over 130 in all three tests but on the last two year's results, he would not have got into Judd or Skinners.

But for the super high scores to be required for the SS's then this throws up three scenarios. Because there can only have been a certain percentage of children (less than 2%) with the high scores (about 250-300 DC total).

1. Either the DC's are all travelling from all over the county.
2. There is a super high concentration of very clever DC in West Kent
3. Knowing that high scores are needed a proportion of the DC have been tutored and coached in the west Kent area more so than the rest of the county skewing the results.

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