S2 ocr mei 31st may statistics 2

You know when you're give the mean and standard deviation and you're asked to sketch the distribution, how do you know how tall it should be? I know the bottom line is basically mean, what is the vertical line for?

Reply 42

NJam

Original post by albus

I know I have to write working out in the exam, but I want to use the calculator to check the answers too.

Does anyone know the meaning of a 5% significance level, and the assumptions made when using Normal approximations to binomial and Poisson distributions.

Im sure 5% significance level is the probability that there is a type 1 error: i.e, that you throw out the wrong hypothesis at the end of your test.

Im not too sure about the assumptions though.. sorry

Edit:

When approximating Normal to Binomial, you are assuming that the distribution has a roughly symmetrical shape, usually given by the fact that n is large and p is around 0.5

When approximating Normal to Poisson, you are assuming that, again, the distribution is roughly symmetrical and that whilst n is infinitely large and p is infinitely small, np (ie lambda) is finite.

You might also want to include that the assumptions are only really accurate enough at n>50, however it is necessary to use it for n>20 (binomial) and n>11 (poisson) as the tables we are given only go this far for their respective values.

Correct me if I am wrong, I hope this helped!

(edited 11 years ago)

Reply 43

Silent--ly

Original post by chocolate_monster

You know when you're give the mean and standard deviation and you're asked to sketch the distribution, how do you know how tall it should be? I know the bottom line is basically mean, what is the vertical line for?

If the standard deviation is large, it will be short and fat, if it is small it'll be tall and thin. Normally they ask you to sketch two on the same axis, and it's effectively just a comparison of the size of their means / deviations.

Reply 44

chunderseverywhere

5

Is it me or are the grade boundaries for an A quite high for this paper? Some of them are even creeping towards 90% in some of the past papers I've done! I think MEI have forgotten how hard their course really is! :')

Reply 45

Original post by chunderseverywhere

Is it me or are the grade boundaries for an A quite high for this paper? Some of them are even creeping towards 90% in some of the past papers I've done! I think MEI have forgotten how hard their course really is! :')

Yeah 66/72 is 90% for M2, M2 is not an easy module either.

Reply 46

skibur

12

really need a ~90 in this, M2 is going to drag me down :frown:

Reply 47

gymrat

7

Original post by albus

Yeah 66/72 is 90% for M2, M2 is not an easy module either.

!

Can't believe the timetable also, M2 and M1 after S2

Reply 48

Original post by chunderseverywhere

Is it me or are the grade boundaries for an A quite high for this paper? Some of them are even creeping towards 90% in some of the past papers I've done! I think MEI have forgotten how hard their course really is! :')

90%? That is really high!
That's 'A' out the question for me..

Reply 49

Really hope we get a good paper tomorrow.. I like the 12marks for χ²test but have been losing marks on the explain each contribution or something.. :| What do you need to include?

Reply 50

Original post by skibur

really need a ~90 in this, M2 is going to drag me down :frown:

What did you get in M2 last time, I got 59/72 which is a D in Jan12.

Reply 51

Original post by Silent--ly

If the standard deviation is large, it will be short and fat, if it is small it'll be tall and thin. Normally they ask you to sketch two on the same axis, and it's effectively just a comparison of the size of their means / deviations.

I asked my teacher and she gave me an equation to work out vertical value
In two or three past papers they have given mark for it, im not sure if we need to know it, but better safe than sorry

(edited 11 years ago)

Original post by chocolate_monster

I asked my teacher and she gave me an equation to work out verticle value
In two or three past papers they have given mark for it, im not sure if we need to know it, but better safe than sorry

Could you point me to a past paper with one of these type of questions please? Im not sure ive seen a question like this before...

Reply 53

Sketching the Normal curve is on June 2011 paper question 3(iv)(B) its worth 4 marks.

Reply 54

Original post by NJam

Could you point me to a past paper with one of these type of questions please? Im not sure ive seen a question like this before...

June 2011
Question 3 iv - B

Jan 2008
Question 3 iii

June 2005
Question 2 iv

On the mark scheme, the values are given for vertical

(edited 11 years ago)

Reply 55

NJam

Original post by albus

Sketching the Normal curve is on June 2011 paper question 3(iv)(B) its worth 4 marks.

Great, thanks! Makes a lot more sense now :smile:

.

Original post by chocolate_monster

June 2011
Question 3 iv - B

Jan 2008
Question 3 iii

June 2005
Question 2 iv

On the mark scheme, the values are given for vertical

Thanks for that, I'll have a go at those now!

(edited 11 years ago)

Reply 56

Has anyone got a Texas Instruments calculator which can work out expected frequency and contributions in a matrix.

Reply 57