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Official Edexcel S3 thread Wednesday 20 May 2015 Morning [6691] watch

1. (Original post by Mutleybm1996)
Which paper?

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June 2011

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2. Does arsey do s3?
3. (Original post by DCMed96)
Hell yeah, they are hard as f*ck

when you use pmcc, do you substitute the ranks into the equation, or substitute the actual values?????
Where do you access the IAL papers?
4. To clarify, if there's a tied rank, do you input the average rank into spearman's correlation or person's correlation?
To clarify, if there's a tied rank, do you input the average rank into spearman's correlation or person's correlation?
pmcc, but i doubt they'll ask us, i quoted the syllabus a few posts back saying that they won't ask us, but might just ask what to do if it is tied rank (which they have once in a prev paper)
To clarify, if there's a tied rank, do you input the average rank into spearman's correlation or person's correlation?
I want to ask the same question as well,.. do you carry out the pmcc test instead and use the original values or the ranks??
7. (Original post by mmms95)
pmcc, but i doubt they'll ask us, i quoted the syllabus a few posts back saying that they won't ask us, but might just ask what to do if it is tied rank (which they have once in a prev paper)
Exactly, they might ask us what to do. What do we say then?
8. can someone pls help me with june 2014 q7b, why is the critical region -2.3263 and not 2.3263?
thnx
Exactly, they might ask us what to do. What do we say then?
Think the 2012 one went something like

They are now tied ranks
Average the ranks and use *formula for PMCC*

Don't think it mentions whether or not you use the ranks or the data; I don't see what the point of first averaging the ranks would be if you were going to use the actual data though
10. (Original post by jsoso)
Does arsey do s3?
no but i can try to make one
(Original post by 13 1 20 8 42)
Think the 2012 one went something like

They are now tied ranks
Average the ranks and use *formula for PMCC*

Don't think it mentions whether or not you use the ranks or the data; I don't see what the point of first averaging the ranks would be if you were going to use the actual data though
indeed, there is no point of using tied ranks if we are not going to use the spearman rank. IN the textbook, they say it is fairly accurate to use spearman with one or two tied ranks because it is not going to make any difference. But since the mark scheme mentioned pmcc, I was slightly confused because is it implying that we should just use pmcc on the orginal set of data (Sxx, Sxy, Syy stuff) instead?

i hope it won't come out tomorrow, but i guess everyone is so stressed now..
11. (Original post by Mina Makin)
can someone pls help me with june 2014 q7b, why is the critical region -2.3263 and not 2.3263?
thnx
You are looking for a less than probability rather than a more than probability: we want to know how likely it is that x could be less than or equal to 999.54 when the mean is assumed to be 1000

Usually we deal with the latter, P(z > 2.3263) = 0.01, but P(z < -2.3263) = 0.01 also
For a one-tailed test you can usually discern the sign of the critical region by the sign of your test statistic
12. Does anyone know which year the paper was which had this tied rank question?
13. (Original post by 13 1 20 8 42)
You are looking for a less than probability rather than a more than probability: we want to know how likely it is that x could be less than or equal to 999.54 when the mean is assumed to be 1000

Usually we deal with the latter, P(z > 2.3263) = 0.01, but P(z < -2.3263) = 0.01 also
For a one-tailed test you can usually discern the sign of the critical region by the sign of your test statistic
Thanks a lot! that makes sense
14. (Original post by DCMed96)
indeed, there is no point of using tied ranks if we are not going to use the spearman rank. IN the textbook, they say it is fairly accurate to use spearman with one or two tied ranks because it is not going to make any difference. But since the mark scheme mentioned pmcc, I was slightly confused because is it implying that we should just use pmcc on the orginal set of data (Sxx, Sxy, Syy stuff) instead?

i hope it won't come out tomorrow, but i guess everyone is so stressed now..
I'm just planning on regurgitating that 2012 answer; if it's there, considering numerical questions won't occur, it can only really be 2 or 3 marks. Also the same answer, however senseless it seems, as they gave back then should surely still suffice
Does anyone know which year the paper was which had this tied rank question?
https://869d950bf149eefd5cd2652b4001...%20Edexcel.pdf

16. Do we need to know this?

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17. (Original post by Mutleybm1996)

Do we need to know this?

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They give you the first formula on the top left hand side and you use that to reach the formula at the end of the page.
18. (Original post by nayilgervinho)
They give you the first formula on the top left hand side and you use that to reach the formula at the end of the page.
So we need to know the proof?

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19. (Original post by Mutleybm1996)
So we need to know the proof?

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Just the formula that s2 = sum of x2 - n lots of the mean squared over (n-1)
20. (Original post by nayilgervinho)
Just the formula that s2 = sum of x2 - n lots of the mean squared over (n-1)
Just the formula?
No proof?

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