There was this, but poss this is from Bucks (need a degree in stats to understand!!!) Sorry lost the source of it and underneath more stuff I found with bit back to the source. Hope it helps.......
It all depends on the ability of the cohort taking the exam. This will affect the standard deviation value of all the scores. This figure varies from year to year. The standard deviation is compiled statistically by finding the mean value of all the cohort scores and then using a statistical formula to find the standard deviation. Once the standard deviation is found then another formula is used to find standardised score.
S = 15(b — a)/sd + 100
b is your child raw score
a is the mean average score
sd is standard deviation
Let's assume that standard deviation of all bucks school last year was 10.2.
Assume your child scored 72 out of 80 and the average score for the cohort was 57.Then to get your child score all you have to do is substitute in the formula above.
S = 15(73 — 57)/10.2 + 100 = 123
123 will be the score but not adjusted to age, which of course is even more complicated. To standardise for age your child will only be compared with his peer group for performance. So lets assume all 10 year old all performed very well, then they will be no points added.
Assume your child raw score is 73, which is 91 %, and the average raw score was 62, which is 73 %. Your standardised score will be lower.
S = 15(73 —62)/10.2 + 100 = 116
you can see from both calculations taht your child score can vary if the mean changes.on both examples he performed well scoring 91%., but his standarised score varied due to the shift in the average score. If the cohort is a very bright bunch, then the mean will rise which will suppress the standardised scores of all the cohert.
Assume you child gets a full raw score. He or she will not be able to achieve the maximum 141. His standardised score will be 126. of cource this will never happen as the average score will never be as high.
S = 15(80—62)/10.2 + 100 = 126
You will never be able to answer your question very accurately as the formula has two dependent variable which varies from year to year and hugely depends on the ability of the cohort.
Slough consortium usually produces a lower mean value to Tiffin’s due the different abilities of the cohorts.
Unfortunately no one including some posters who I thought might know more/better replied, they simply posted around me! I've seen your question a couple of months(?) ago and thought 1 or 2 perhaps would provide the answer.
My recollection tells me that there is no way to translate percentage marks to the standardised score, or vice versa. I'll leave aside the adjustment for age differences of students for the moment. The act of standardisation takes the raw marks and maps them to points on a specific selected Normal Distribution curve. This means that whether you score 70 or 95, if your mark was the top mark it will be mapped to the full 140 out of 140. So it emphasises the position within the group of students sitting the exam rather than the absolute score, hence why no connection.
Hope that helps rather than confuses!
I hope this explains it.[/quote]