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# **AQA Stats Quesion help** Watch

1. Hi,

Guys I am trying work out a set of questions but have no clue of working them
out.

Would greatly appreciated if someone can work out the answers and maybe even explain?

1. Draw separate scatter diagrams, each with about six points, for which the product moment correlation coefficients R are

ii. close to zero

iii. equal to 1

2. for seven pairs of values of the random variables X and Y

SUM of x= 147 SUM of x= 252 SUM of x= 5611 SUM of x= 3307 SUM of x= 10028

Calculate correlation coefficients between X and Y

3. Reading, X 4 10 9 7 6 5 7 9 8 6
Spelling, Y 8 6 10 5 8 4 8 9 7 4

i) Draw a scatter diagram and tell wheather there appears to be any linear correlation

ii) Calculate correlation coefficients and compare this with your assertion based on the scatter diagram

4. Six pairs of values of X and Y are shown in the table:

X 4 a 7 a+3 10 12
Y 19 17 3b 11 9 b

i) mean = 8 and sum of y squared= 1012 calculate the values of a and b

ii) calculate the products moment correlation coefficient

5. Plot a scatter diagram for the following set of points

(2.4,7.9), (3.7,16.5), (5.6,13.6),(4.1,9.5),(8.2,18.2), (6.3,12.5),(3.0,5.6),

i) calculate the product momment correlation coefficient

ii) it is suspected that one of these points is an outlier. which point is it likely to be? calculate the product momment correlation coefficient for the remaining six points.

Please reply on here or via PM or on my email at [email protected]

People who work it out for me will get a prize or reward!
2. Please remember not to post full answers, only hints. If you are unsure of the posting guide please see the annoucement
(Original post by lionyo)
.
I would like you to read this too as a new user please and maybe edit your post a bit to reduce the number of questions. Also please take note of my edit.
3. 1i The correlation has to be positive but very weak, so draw the points so that they roughly go from bottom left to top right but are scattered around a lot

ii Put them in a symmetrical pattern so that there is no positive or negative correlation. As long as you don't draw the points accurately, the correlation will be close to but not exactly zero

iii Put the points exactly in a straight line with positive gradient

iv Put the points roughly in a straight line with negative gradient

2 You just have to plug numbers into a formula here. If you can't remember the formula for correlation then look it up

3 i You should be able to draw a scatter diagram

ii Calculate the sum of x, sum of x squared etc then answer this question in a similar way to question 2

4 i Calculate the mean and sum of y squared yourself using the given data. Then make them equal to 8 and 1012 respectively. This should give you two equations which you can solve to get a and b.

ii You'll need the sum of x squared and sum of y which you'll have to add up yourself from the data. Then calculate correlation using its formula.

5 i Similar method to previous questions

ii Use the scatter diagram to decide which point is the outlier, then delete that point and calculate correlation again.

Try this and if you get stuck with anything post what's difficult to get more help.

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Updated: December 13, 2010
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