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Date November 2020 Marks available 3 Reference code 20N.1.AHL.TZ0.F_13
Level Additional Higher Level Paper Paper 1 Time zone Time zone 0
Command term Predict Question number F_13 Adapted from N/A

Question

Observations on 12 pairs of values of the random variables X, Y yielded the following results.

x=76.3, x2=563.7, y=72.2, y2=460.1, xy=495.4

Calculate the value of r, the product moment correlation coefficient of the sample.

[3]
a.i.

Assuming that the distribution of X, Y is bivariate normal with product moment correlation coefficient ρ, calculate the p-value of your result when testing the hypotheses H0: ρ=0 ; H1: ρ>0.

[3]
a.ii.

State whether your p-value suggests that X and Y are independent.

[1]
a.iii.

Given a further value x=5.2 from the distribution of X, Y, predict the corresponding value of y. Give your answer to one decimal place.

[3]
b.

Markscheme

use of

r=xy-nx¯y¯x2-nx¯2y2-ny¯2        M1

=495.4-12×76.312×72.212563.7-12×76.32122460.1-12×72.22122        A1

=0.809        A1


Note:
Accept any answer that rounds to 0.81.


[3 marks]

a.i.

t=0.80856101-0.808562         (M1)

=4.345        A1

p-value =7.27×10-4        A1


Note:
Accept any answer that rounds to 7.2 or 7.3×10-4.

Note: Follow through their p-value


[3 marks]

a.ii.

this value indicates that X,Y are not independent       A1


[1 mark]

a.iii.

use of

y-y¯=xy-nx¯y¯x2-nx¯2x-x¯       M1

y-72.212=495.4-12×76.312×72.212563.7-12×76.32122x-76.312       A1

putting  x=5.2  gives  y=5.5       A1


[3 marks]

b.

Examiners report

[N/A]
a.i.
[N/A]
a.ii.
[N/A]
a.iii.
[N/A]
b.

Syllabus sections

Topic 4—Statistics and probability » AHL 4.17—Poisson distribution
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Topic 4—Statistics and probability

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