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S2 ocr mei 2016
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Why bother with a post grad? Are they even worth it? Have your say!  26102016 

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 1
 15062016 11:14

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 2
 15062016 11:19
Okay, what did you get for your rank correlation?

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 3
 15062016 13:00
For the first question, (scatter graph) what did people use as the vertical and horizontal axis? I used percentage as the y axis because it seemed logical to me but I'm not so sure now!
What is the assumption needed for spearman's rank. Some people said they put 'no assumption' as the answer but I just guessed at bivariate normal distribution because the PMCC is similar...
I screwed up 3iv really badly with the simultaneous equations to find the mean and SD, but luckily I had time to redo it in the extra space and got 46040 for the mean... If I remember correctly, and 5509 for the SD? (To 4sf)
Was quite happy with all of the hyp tests, can't remember what results I got though, although for the last one I did a silly and calculated the SD as npq which came out as 52.8 I think... I got a sensible answer though so I'm not sure if that's right or not.
Hope this helps! 
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 4
 15062016 13:07
(Original post by Osmium)
Okay, what did you get for your rank correlation?Post rating:2 
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 5
 15062016 13:08
I have no idea why I was getting the postive of that value after two attempts. Could be because I was ranking in reverese.

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 6
 15062016 15:11
(Original post by Osmium)
I have no idea why I was getting the postive of that value after two attempts. Could be because I was ranking in reverese.
(6xEd^2)/n(n^21) 1
when it is supposed to be
1 (6xEd^2)/n(n^21)
That would give you 0.664, but don't worry, you will still get marks for ranking, getting Ed^2 and using the main part of the formula!
Ranking in reverse is still right as long as you use the same method (lowhigh or higlow) for both variables. Because the values are then squared so it doesn't matter if they are pos or neg.Last edited by eturtle182; 15062016 at 15:13. 
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 7
 15062016 16:44
I forgot to square the mean for final hypothesis testing when calculating the variance.
Messed up the standard deviation, mean + distribution diagrams in qs 3 (right method, wrong values and therefore wrong diagram).
Messed up a Normal calc worth 3 marks (method marks maybe?)
Did not draw the scatter diagram in 1 but labelled the axes.
Used Normal to the Poisson instead of to the Binomial.
What grade do you think I'd get? I know it's entirely dependent on the grade boundaries but based on what you think they might be, I'd like an idea of how badly I've done.Last edited by 89911998a; 15062016 at 16:46. 
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 8
 15062016 17:40
(Original post by 89911998a)
I forgot to square the mean for final hypothesis testing when calculating the variance.
Messed up the standard deviation, mean + distribution diagrams in qs 3 (right method, wrong values and therefore wrong diagram).
Messed up a Normal calc worth 3 marks (method marks maybe?)
Did not draw the scatter diagram in 1 but labelled the axes.
Used Normal to the Poisson instead of to the Binomial.
What grade do you think I'd get? I know it's entirely dependent on the grade boundaries but based on what you think they might be, I'd like an idea of how badly I've done.
For the standard deviation, mean and distribution diagram question I'm pretty sure they will give you method marks if you are incorrect, and they would probably mark the diagram using your current value and see if it matches up. It would be pretty horrible if they instantly gave you no marks for not using values that you were meant to get. All in all, about 2 marks as well? (Assuming that your diagram is good and drawn according to the standard deviation and mean YOU got.
Depends on what the normal calculation was, how did you mess up?
By labelled the axes do you just mean put "% population" and "fertiliser use" in the graph? If so you lost 2 marks I think.
Which question was this? Or do you mean approximating to the Normal Distribution via Poisson or Binomial?
All in all, even I don't know what grade you'll get lol, I made stupid mistakes this paper too which might bump me out of a standard A grade on this paper. I already have 5 marks I know I have lost for stupid reasons + I also don't completely know how the diagram question will work since like you I calculated sigma and the mean wrong, but with the right method.Last edited by Studious_Student; 15062016 at 17:44. 
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 9
 15062016 17:56
hey guys,
i accepted Ho on all of the tests, what about you?
i also plotted the %on the x axis and fertiliser on the y axis , is that wrong? 
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 10
 15062016 18:05
(Original post by Yasmine Grizel)
hey guys,
i accepted Ho on all of the tests, what about you?
i also plotted the %on the x axis and fertiliser on the y axis , is that wrong?
variance was sxx/n1,(n1 being 59) and variance for the hypothesis test was Sxx/((n1)*60) 
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 11
 15062016 18:31
I rejected the null hypothesis for the last question bang!
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 12
 15062016 18:31
for question 3iv) for mean i got 50350 (or something close) and for sd i got about 6000 something can't remember the exact values of either but both mean and sd were higher than the given distribution mean and sd, did anyone have similar answer as me? :/

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 13
 15062016 18:34
(Original post by Tajwar786)
for question 3iv) for mean i got 50350 (or something close) and for sd i got about 6000 something can't remember the exact values of either but both mean and sd were higher than the given distribution mean and sd, did anyone have similar answer as me? :/ 
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 14
 15062016 19:48
Anyone know how the sketching normal distributions question will be marked? I labelled the horizontal axis with the means, and made sure the distribution with the larger variance was shorter and fatter, but apart from that I didn't know what to do...

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 15
 15062016 20:07
(Original post by Ting07251997)
i remember for the last question i got a significant result of the probability for the mean to be greater than 373/60, to be 0.52% therefore significant
variance was sxx/n1,(n1 being 59) and variance for the hypothesis test was Sxx/((n1)*60) 
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 16
 15062016 20:19
definitely for the H0 and H1, but not sure whether they will give you the calculation method marks because your variance doesn't seem like it was correct meaning that unless there is error carry forward mark which there some time is then you would probably get max 6 marks, otherwise 3 for H0 and H1 and if you have defining mull as the population mean of the given context of the question

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 17
 15062016 20:33
(Original post by Yasmine Grizel)
hey guys,
i accepted Ho on all of the tests, what about you?
i also plotted the %on the x axis and fertiliser on the y axis , is that wrong? 
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 18
 15062016 21:03
This is what I can remember
Q1catter diagram:
1 mark for labelled axes, 2 marks for correctly plotted points
Spearmans: 0.366
Spearmans hypothesis test: accept H0.
Pearsons not appropriate since not bivariate normal because not elliptical.
No assumptions required for Spearmans.
1% significance level is 1% probability of rejecting H0 when it is in fact true.
Q2:
Independent: mutations dont affect probability of another mutation, random:mutations are unpredictable
Binomial calculation: 20C1 x 0.012^1 x 0.988^19 or something like that
Approximation to posission: mean = 500x0.012, then use tables etc.
Approximation to normal, mean=50000x0.012, variance=50000x0.012x0.998 then standardise and use tables etc.
Q3:
Simple normal calculations
Manufacturer claims over 95% etc.: calculate value= 0.9502 so claim is true.
Find sigma and mu, sigma =6350 and mu = 60500 or 50850 or something like that?
Draw distributions: X has lower mean and variance so less spread but taller
Calculate value of h when 99.9%: I got 40500 or there abouts
Q4:
Calculate expected frequency of female and likes maths, show contribution=...
Chi test, add up contributions, accept H0.
Normal test, calculate mean and variance or standard distribution, calculate test statistic, reject H0.
If any one remembers anything else let me know. 
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 19
 15062016 21:08
(Original post by ROSS1998JONES2)
This is what I can remember
Q1catter diagram:
1 mark for labelled axes, 2 marks for correctly plotted points
Spearmans: 0.366
Spearmans hypothesis test: accept H0.
Pearsons not appropriate since not bivariate normal because not elliptical.
No assumptions required for Spearmans.
1% significance level is 1% probability of rejecting H0 when it is in fact true.
Q2:
Independent: mutations dont affect probability of another mutation, random:mutations are unpredictable
Binomial calculation: 20C1 x 0.012^1 x 0.988^19 or something like that
Approximation to posission: mean = 500x0.012, then use tables etc.
Approximation to normal, mean=50000x0.012, variance=50000x0.012x0.998 then standardise and use tables etc.
Q3:
Simple normal calculations
Manufacturer claims over 95% etc.: calculate value= 0.9502 so claim is true.
Find sigma and mu, sigma =6350 and mu = 60500 or 50850 or something like that?
Draw distributions: X has lower mean and variance so less spread but taller
Calculate value of h when 99.9%: I got 40500 or there abouts
Q4:
Calculate expected frequency of female and likes maths, show contribution=...
Chi test, add up contributions, accept H0.
Normal test, calculate mean and variance or standard distribution, calculate test statistic, reject H0.
If any one remembers anything else let me know. 
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 20
 15062016 21:18
(Original post by Studious_Student)
Just as a note to other people, you would also get the marks if you approximated to normal using Poisson distribution, it would just be X~N(600,600)
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Updated: June 21, 2016
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