Edexcel S3 - Wednesday 25th May AM 2016

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Even though S3 is over, I thought I'd share an interesting expectation algebra question from the IAL paper with everyone. :biggrin:

I think the question went something like this:

Given that

\mathrm{E\left ( S^{2} \right )}

is an unbiased estimator of

\sigma^{2}

, and the data obtained is from a population with mean

\mu

and variance

\sigma^{2}

, show that

\displaystyle \mathrm{Y = \frac{1}{8}\left ( \sum_{i=1}^{8}X_{i}^{2}-8\bar{X}^{2} \right )}

is a biased estimator of

\sigma^{2}

.

@Krollo, @physicsmaths - you guys might like this.

(edited 7 years ago)

Reply 1441

username1162972

Original post by Krollo

Weird thing is, I would probably be a lot less stressed about exams if I knew I'd dropped marks already... at the moment it seems teachers / friends / folk online are kind of expecting me to get full ums again when I know it isn't realistically possible. Knowing that I've already dropped marks can make things much easier, since beyond that A Levels serve little real purpose for me provided I don't completely **** them up.

My brain is a strange place, sorry for pouring it out onto the s3 thread guys :tongue:

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I know what you mean but except people expect me to get kill every module(not 100 but like 90+) little do they know I always do the bare minimum to get the grade needed like in D2 i will learn one chapter to get the 10 ums i need. I hate maths modules tbh, i don't have consistency even in FP and mechanics to get straight raw 100s due to not paying enough attention to mark schemes.

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Reply 1442

Zacken

Original post by Krollo

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S'alright mate, just work your ass off for meeting your offer and nobody is going to care about UMS. You're already meme-worthy. :lol:

Reply 1443

username1162972

Original post by Ayman!

Even though S3 is over, I thought I'd share an interesting expectation algebra question from the IAL paper with everyone. :biggrin:

I think the question went something like this:

Given that

\mathrm{E\left ( S^{2} \right )}

is an unbiased estimator of

\sigma^{2}

, and the data obtained is from a population with mean

\mu

and variance

\sigma^{2}

, show that

\displaystyle \mathrm{Y = \frac{1}{8}\left ( \sum_{i=1}^{8}X_{i}^{2}-8\bar{X}^{2} \right )}

is a biased estimator of

\sigma^{2}

.

@Krollo, @physicsmaths - you guys might like this.

Biased or unbiased?
Where have i gone rong
ImageUploadedByStudent Room1464264263.630770.jpg

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Reply 1444

Krollo

Original post by Ayman!

Even though S3 is over, I thought I'd share an interesting expectation algebra question from the IAL paper with everyone. :biggrin:

I think the question went something like this:

Given that

\mathrm{E\left ( S^{2} \right )}

is an unbiased estimator of

\sigma^{2}

, and the data obtained is from a population with mean

\mu

and variance

\sigma^{2}

, show that

\displaystyle \mathrm{Y = \frac{1}{8}\left ( \sum_{i=1}^{8}X_{i}^{2}-8\bar{X}^{2} \right )}

is a biased estimator of

\sigma^{2}

.

@Krollo, @physicsmaths - you guys might like this.

Looks interesting. Before I get started is the 8xbar^2 within the summation, if you see what I mean?

Reply 1445

Zacken

Original post by Krollo

Looks interesting. Before I get started is the 8xbar^2 within the summation, if you see what I mean?

Nope.

Don't get too interested, it's only 2 marks. :tongue:

Reply 1446

username1162972

Original post by Zacken

Nope.

Don't get too interested, it's only 2 marks. :tongue:

Did i get it rite

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Reply 1447

Zacken

Original post by physicsmaths

Did i get it rite

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Nah.

Reply 1448

username1162972

Original post by Zacken

Nah.

Fukin statistics. ********, the question is rong thats y. Mandem is sick

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Reply 1449

Zacken

Remember that if

S^2

is an unbiased estimator of

\sigma^2

then

7S^2 = \sum_{i=1}^8 X_i - 8\bar{X}

Reply 1450

Ayman!

Worded the question slightly wrong; E(S^2) = sigma^2. :ninja:

Reply 1451

username1162972

Dis questions bare hard.
Man is baffed bruv.
Gna go do some step ii stats to make myself feel gud

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Reply 1452

Zacken

S3 model solutions here

Reply 1453

tazza ma razza

This is late... oh well

what are we thinking boundaries are for this paper (A*-B) almost certain i got 65+ and am hoping it is at least 80 ums. Thanks

Reply 1454

username1162972

Original post by tazza ma razza

This is late... oh well

what are we thinking boundaries are for this paper (A*-B) almost certain i got 65+ and am hoping it is at least 80 ums. Thanks