Bell Curve - To remove or not to remove?
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Well said.
At home, parents play a big part. In school the teachers should too. -
AWSP:
The Bell Curve's evil is in the distortion in weighting. Mother Tongue becomes the heaviest weighted apparently because of the 'profile' of the cohort. A very apparent symptom from past years observation is that is that the top scorers have typically very strong command of second language. You do not see top scorers who demonstrate strong maths or science or english skills over the rest of the subjects. You may also try to guess the profile of last years top scorers which coincidentally has a \"significant\" number of Malay students. The distribution in Mother tongue is most logically not a bell curve but a hump shaped curve or a very left skewed distribution. A skewed distribution will create a lot of distortion. I think this part is totally unforeseen by the folks in MOE and they are not willing to admit the problem.
Based on immigration trend, I would place a bet that this years top 10 scorers will have a good representation by Tamil students. (Another skewing effect).
To the more statistically trained people, I am saying that 3rd moment effect is quite logically present given our children's profile in mother tongue. The disortionary effect is worse and more drastic than the 2nd moment effect(standard deviation).
The pressure in PSLE is not due to T-score but the competitive entry into the top IP school with limited placing. It doesnt matter which way you design your scoring as long as demand exceed supply by a huge mile.
my gal used to be top 6 in her std even though her MT was not very strong. and for psle she was the 15 th top in her sch and students who took Malay as MT got better T-score than her even though in sch exams these students used to be 20+ in std. I don't understand how and why. I assume it's because for MT as there are several sub-populations and the mean score and std deviation differ, this has an advantage for 1 or 2 sub- population over the rest. as for MT shouldn't MOE use raw score? -
lotus123:
by the way my gal's MT is Tamil . also I have noticed that even last year's top 2 Indian students took Malay has 2nd Lang and not Tamil. even several years ago in 2005 or 2006 I can't remember the Indian gal from raffles pri took Malay as 2nd Lang and not Tamil. even my daughter's classmate in the top class as my gal but with very strong command of Tamil Lang didn't get a very high T-score for psle . so I think from all these I can deduce that Students with very good command of Malay language and in the top class of a sch will emerge as that sch's psle top scorer or get a relatively higher T-score than her peers even though they may hav very similar raw scores. maybe it has to do with the mean score and std deviation. also I have been told by Tamil teachers they have been told to mark Tamil papers very strictly ever since they modified psle Tamil curriculum a few years ago. this poses an added disadvantage to Tamil students like my gal whose command of Tamil Lang is not very good as my hubby is not Tamil and we speak English at home. also during my daughter's time in primary school she was not allowed to take Malay or other languages for MT unless it's mother tongue. but now MOE has relaxed this rule and students can take any MT langs.AWSP:
The Bell Curve's evil is in the distortion in weighting. Mother Tongue becomes the heaviest weighted apparently because of the 'profile' of the cohort. A very apparent symptom from past years observation is that is that the top scorers have typically very strong command of second language. You do not see top scorers who demonstrate strong maths or science or english skills over the rest of the subjects. You may also try to guess the profile of last years top scorers which coincidentally has a \"significant\" number of Malay students. The distribution in Mother tongue is most logically not a bell curve but a hump shaped curve or a very left skewed distribution. A skewed distribution will create a lot of distortion. I think this part is totally unforeseen by the folks in MOE and they are not willing to admit the problem.
Based on immigration trend, I would place a bet that this years top 10 scorers will have a good representation by Tamil students. (Another skewing effect).
To the more statistically trained people, I am saying that 3rd moment effect is quite logically present given our children's profile in mother tongue. The disortionary effect is worse and more drastic than the 2nd moment effect(standard deviation).
The pressure in PSLE is not due to T-score but the competitive entry into the top IP school with limited placing. It doesnt matter which way you design your scoring as long as demand exceed supply by a huge mile.
my gal used to be top 6 in her std even though her MT was not very strong. and for psle she was the 15 th top in her sch and students who took Malay as MT got better T-score than her even though in sch exams these students used to be 20+ in std. I don't understand how and why. I assume it's because for MT as there are several sub-populations and the mean score and std deviation differ, this has an advantage for 1 or 2 sub- population over the rest. as for MT shouldn't MOE use raw score? -
AWSP:
Feeder School System is not a fair system. No matter how one might argue about preserving culture or parents' contribution to the school as most parents and students who benefit will proposition.kamom:
The T-score for feeder schools is always lower for their own kind but higher for 'outsiders'. I always wonder if it is fair.
A child with a T-score of 200 can get into their feeder school.
A child wth a T-score of 220 can't get in cos' no \"connection\".
If a T-score of 220 cannot thrive in the school, how can a T-score of 200 survive???
It is not fair because it is not available as an option to the entire cohort no matter the background. Take those born to poorer families for example.
Likewise for DSA. Although my child benefitted from it. I will say without hesitation that it is not fair as it is not an option for those whose parents lack the means, knowledge and resources to go through the exercise.
I am disappointed with last week's talking point on whether DSA is fair. An MP whose child DSAed into a top school, went on to contend that it is fair and good because it takes away the stress for his child who may fumble in PSLE. I cannot see anyone could have ignored the fact that there is a majority out there for whom DSA is not an option.
but we must remember that students who get into schools like RI and RGS and even other IP schools via DSA sports may not be allowed to continue their 5th and 6th years at RI if they don't do well academically. which means these students win trophies for the schools for sports but may be kicked out if the schools think they won't be able to cope at JC. these kids without their GCE O levels have to switch to poly or other JCs. -
SAHM_TAN:
Don't know if this anecdote is relevant. A national gymnat got into a top school through DSA. I remembered T-score was less than 230. Life was tough because need to train 24/7 and to catch up with the others. Always among the last few in class in tests and exams. Cannot give up sport because that was the condition for DSA.Will a student who score 220 be able to thrive in RI? Assuming that 220 is consistent with the child's academic performance in school.
Wanted to quit top school and go poly but was persuaded by friends to hang in there. Scrapped through year 4 IP (by appeal I remembered) and reached JC. No longer need to continue with sport and has more time for study. Finally gotten AAABB for A level. Not a great score for that school but quite a remarkable achievement for that person's academic ability.
Moral of the story : Dip in red ink becomes red. Dip in black in becomes black. Mencius mummy shifted house 3 times so that he can be under the influence of good environment. -
lotus123:
No lah, they not so bad one. Unless the kid is defiant with poor attitude, sure can go year 5 and 6. So far I haven't kay poh any top sports guys being kicked out because of poor results. Extend for 1 more year so that they can focus on their sports have - many of them. Scholars sent home because of poor results, yes.but we must remember that students who get into schools like RI and RGS and even other IP schools via DSA sports may not be allowed to continue their 5th and 6th years at RI if they don't do well academically. which means these students win trophies for the schools for sports but may be kicked out if the schools think they won't be able to cope at JC. these kids without their GCE O levels have to switch to poly or other JCs.
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lotus123:
I find the T-score formula very interesting and have been playing with it. Lets look at the following situations :
my gal used to be top 6 in her std even though her MT was not very strong. and for psle she was the 15 th top in her sch and students who took Malay as MT got better T-score than her even though in sch exams these students used to be 20+ in std. I don't understand how and why. I assume it's because for MT as there are several sub-populations and the mean score and std deviation differ, this has an advantage for 1 or 2 sub- population over the rest. as for MT shouldn't MOE use raw score?
Situation 1
Mean = 75 higher average means EASY paperand SD = 13
For raw score of 100, T score = 69 pts
For raw score of 50, T score = 31pts (it is LESS than half of 69 pts - the T score for 100 marks)
Situation 1
Mean = 60 lower average means DIFFICULT paperand SD = 13
For raw score of 100, T score = 81 pts
For raw score of 50, T score = 42.5pts (it is MORE than half of 82 pts - the T score for 100 marks)
Therefore, the mean, i.e. the level of difficulty of the paper will affect the T-score. Imho, T-score can stay but not the current way of ranking by aggregate T-score (where the T-score of each subject is added up.) They should use the Total Raw Score to convert to T-score for ranking the students. In this way, the advantage of a low mean (as in MT paper) will be shared by all. Similarly, the effect of a high mean will also be applied to all. -
When the paper is easy, the mean will be higher but the SD will be smaller, isnt it?
When the paper is difficult, mean will be low but SD will be bigger, am I right?
So it is hard to say how the t-score will be affected? Yes or no? -
PiggyLalala:
I remembered that the trend is still the same. Lets see these new situations :When the paper is easy, the mean will be higher but the SD will be smaller, isnt it?
When the paper is difficult, mean will be low but SD will be bigger, am I right?
So it is hard to say how the t-score will be affected? Yes or no?
Situation 1
Mean = 75 higher average means EASY paper and SD = 11 (smaller DS)
For raw score of 100, T score = 73 pts
For raw score of 50, T score = 27.5pts (it is MUCH LESSER than half of 73 - the T score for 100 marks)
Situation 2
Mean = 60 lower average means DIFFICULT paper and SD = 14 (bigger SD)
For raw score of 100, T score = 79 pts
For raw score of 50, T score = 43 pts (it is MUCH MORE than half of 79 pts - the T score for 100 marks)
The SD can change. But the trend on how the mean will affect the T-score of those people with marks below the mean score remains the same. That is, when the mean is low, those below the average will suffer a bigger lost in T-score while if the mean is high, those below the average suffer a smaller lost in T-score.
Lets create this hypothetical case study for 2 subjects using the above set of data :
Math
Mean = 75 higher average means EASY paper and SD = 11 (smaller DS)
Candidate Ah Kow gets 100 marks, T score = 73 pts
Candidate Bob gets 50 marks, T score = 27.5pts
English
Mean = 60 lower average means DIFFICULT paper and SD = 14 (bigger SD)
Candidate Bob gets 100 marks, T score = 79 pts
Candidate Ah Kow gets 50 marks, T score = 43 pts
Aggregate T-score of Ah Kow = 73 + 43 = 116 pts
Aggregate T-score of Bob = 27.5 + 79 = 106.5 pts
Note that both Ah Kow and Bob have the same total raw score of 150 marks. However, due to the use of aggregate T-score, Bob lost to Ah Kow because he did badly in an easy paper.
Moral of the story : The marks of a paper where everyone does well i.e. high average (e.g. math and Chinese) are much more precious than those of English and Science. -
Interesting, very interesting indeed. I wonder if the scholar/s sitting in a cushy office coming up with all kinds of policies can see the way you all see.
The best way is to do away with T-score and follow the \"O\" levels way...
A* - 1
A - 2
B - 3
C - 4
D - 5
E - 6
Easy and completely transparent.
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