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# Edexcel S3 - Wednesday 25th May AM 2016 watch

1. (Original post by economicss)
Just to check, if one our expected frequencies came out to 5 exactly, this wouldn't be combined right, we only combine values less than 5?! Thanks :-)
this is fine, i wouldn't group it with another colomn etc
2. Can someone make an S2 thread as well?
3. Is maximum likelihood estimators a part of S3 or S4?
4. (Original post by ServantOfMorgoth)
Is maximum likelihood estimators a part of S3 or S4?
Not as far as I am aware.

All you need to do is find the joint distribution of all of the observations in terms of the parameter, xi, log it if necessary, differentiate it with respect to the parameter and solve that, before differnetiating again to check that it is a maximum. Slightly more complicated if it involves two parameters.

(Original post by Ayman!)
Can someone make an S2 thread as well?
If no one else has, I can try
5. (Original post by SeanFM)
If no one else has, I can try
Sean, you're back! Where have you been? And go ahead if it's not too much trouble
6. (Original post by SeanFM)
Not as far as I am aware.

All you need to do is find the joint distribution of all of the observations in terms of the parameter, xi, log it if necessary, differentiate it with respect to the parameter and solve that, before differnetiating again to check that it is a maximum. Slightly more complicated if it involves two parameters.
So it isn't an a level topic?
7. (Original post by ServantOfMorgoth)
So it isn't an a level topic?
Not as far as I am aware, for Edexcel at least.

(Original post by Ayman!)
Sean, you're back! Where have you been? And go ahead if it's not too much trouble
Uni work
8. (Original post by SeanFM)
Not as far as I am aware, for Edexcel at least.

The derivation for the normal distribution MLE for the mean is very confusing.
9. (Original post by ServantOfMorgoth)
The derivation for the normal distribution MLE for the mean is very confusing.
10. (Original post by SeanFM)
I closed that exact same page a few mins ago. I'm not required to know how to derive for 2 unknowns and they don't have an example with only the mean.
11. (Original post by ServantOfMorgoth)
I closed that exact same page a few mins ago. I'm not required to know how to derive for 2 unknowns and they don't have an example with only the mean.
I think you can just treat sigma as a constant and use what they've done for the mean.
12. (Original post by SeanFM)
I think you can just treat sigma as a constant and use what they've done for the mean.
Haha yeah, I figured it out. Thanks
13. https://ee3a68c993d24792ee12a4f9f960...%20Edexcel.pdf

Everything is fine for the very last part of the last question except I used a continuity correction but the mark scheme doesn't use this. Why is this?
I did it slightly differently where I would Reset the Q to P(no of sixes is more than 180)
Then I did P(X1+...+X100>180.5) I rechecked if I had just done P(X1+...X100>180) then I would have got the correct answer.
14. I'm a statistics expert in S1- 4 now. Thanks uni

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15. (Original post by Rkai01)
https://ee3a68c993d24792ee12a4f9f960...%20Edexcel.pdf

Everything is fine for the very last part of the last question except I used a continuity correction but the mark scheme doesn't use this. Why is this?
I did it slightly differently where I would Reset the Q to P(no of sixes is more than 180)
Then I did P(X1+...+X100>180.5) I rechecked if I had just done P(X1+...X100>180) then I would have got the correct answer.
You don't need to use a continuity correction after using in the central limit theorem in Edexcel S3
16. (Original post by Rkai01)
https://ee3a68c993d24792ee12a4f9f960...%20Edexcel.pdf

Everything is fine for the very last part of the last question except I used a continuity correction but the mark scheme doesn't use this. Why is this?
I did it slightly differently where I would Reset the Q to P(no of sixes is more than 180)
Then I did P(X1+...+X100>180.5) I rechecked if I had just done P(X1+...X100>180) then I would have got the correct answer.
The continuity correction is only for when you do the approximations

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17. (Original post by Ayman!)
You don't need to use a continuity correction after using in the central limit theorem in Edexcel S3
In the book it does say a continuity correction can be applied depending on a question. It is definitely in the chapter 3 somewhere in a red box where they write comments.
18. (Original post by ServantOfMorgoth)
The continuity correction is only for when you do the approximations

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But it is an approximation? We are going from binomio to normal
19. The june 2015 paper is beautiful.
20. (Original post by Rkai01)
But it is an approximation? We are going from binomio to normal
But you have already used Central linit theorem.

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