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# Official Thread: OCR MEI S2/M1 Watch

1. Actually think that went incredibly well. Grade boundaries will be as high as last year's at least. When I get home to a computer I'll be up for any queries anyone has etc, plus I might have lost a couple marks so I need to check them out too
2. is the appromximation question to binomial or poisson?
3. (Original post by Bellbird)
is the appromximation question to binomial or poisson?
Poisson.
4. (Original post by Studious_Student)
Poisson.
aw i got it wrong....
5. (Original post by Bellbird)
aw i got it wrong....
I think I got the sigma and Mean question wrong as well lol so don't worry about it, I'll still get method marks but it is a really stupid mistake to make.
6. No its bionomial to normal
7. For why is Poisson a good approximation distribution? I put:

number of possible genes mutating is large and probability of a gene mutating is small.
Hence normal is good approximation to binomial (I meant to say Poisson will I lose both marks)?
8. (Original post by Lollolololololol)
For why is Poisson a good approximation distribution? I put:

number of possible genes mutating is large and probability of a gene mutating is small.
Hence normal is good approximation to binomial (I meant to say Poisson will I lose both marks)?
Cant you just right n is large, p is small???
9. (Original post by QS2Nabz)
http://www.mei.org.uk/files/pdf/spearmanrcc.pdf

"words to make the point that the test is for association in the population by adding thewords “in the underlying population” to the end of the statement about the null hypothesis,making it something like0: There is no association between the variables in the underlying population."

it says here in notes from MEI themselves to write 'underlying population', then why does it condone it in the mark scheme ?
The 2014 Paper also notes "NB Hypotheses must be in context. H0: no association, H1: positive association, earns SC1. Hypotheses must not be given in terms of ρ or mention correlation.", but the textbook writes correlation and uses ρ.

OCR makes the paper and examines. To me it seems as though they just ignore MEI or their course materials.
10. (Original post by Lollolololololol)
For why is Poisson a good approximation distribution? I put:

number of possible genes mutating is large and probability of a gene mutating is small.
Hence normal is good approximation to binomial (I meant to say Poisson will I lose both marks)?
If you just made a reference to n being large and p being small you should get at least 1 mark. Another thing you could have said is that np < 10
11. (Original post by emma_1111)
How were we meant to do the last one? I worked out the sd by doing the variance then square rooting and then placing into equation for the mean?
You should know the equation for sd, it's assumed knowledge from S1...
12. (Original post by AliWilson96)
You should know the equation for sd, it's assumed knowledge from S1...
I used sqrt of (Ex^2 -n times mean^2) / n-1
13. (Original post by Osmium)
The 2014 Paper also notes "NB Hypotheses must be in context. H0: no association, H1: positive association, earns SC1. Hypotheses must not be given in terms of ρ or mention correlation.", but the textbook writes correlation and uses ρ.

OCR makes the paper and examines. To me it seems as though they just ignore MEI or their course materials.
You give hypos in terms of p in the product moment test, spearmans you need to write them in context e.g there is no/a negative association between population percentage and fertiliser use in the underlying population
14. With the 95% claim question, everyone found that to be valid right? I got 0.9502 for the probability making it valid?
15. (Original post by emma_1111)
I used sqrt of (Ex^2 -n times mean^2) / n-1
Exactly
16. (Original post by emma_1111)
I used sqrt of (Ex^2 -n times mean^2) / n-1
Should've been 1.74 from memory?..
17. (Original post by AliWilson96)
With the 95% claim question, everyone found that to be valid right? I got 0.9502 for the probability making it valid?
Yes I got that too.
18. (Original post by AliWilson96)
You give hypos in terms of p in the product moment test, spearmans you need to write them in context e.g there is no/a negative association between population percentage and fertiliser use in the underlying population
Yes. My point is that the textbook uses p and correlation. Have you noticed that?
19. (Original post by AliWilson96)
Should've been 1.74 from memory?..
Yeah I got 1.74

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