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Date May 2017 Marks available 1 Reference code 17M.3sp.hl.TZ0.5
Level HL only Paper Paper 3 Statistics and probability Time zone TZ0
Command term State Question number 5 Adapted from N/A

Question

A teacher decides to use the marks obtained by a random sample of 12 students in Geography and History examinations to investigate whether or not there is a positive association between marks obtained by students in these two subjects. You may assume that the distribution of marks in the two subjects is bivariate normal.

He gives the marks to Anne, one of his students, and asks her to use a calculator to carry out an appropriate test at the 5% significance level. Anne reports that the pp-value is 0.177.

State suitable hypotheses for this investigation.

[1]
a.

State, in context, what conclusion should be drawn from this pp-value.

[1]
b.

The teacher then asks Anne for the values of the tt-statistic and the product moment correlation coefficient rr produced by the calculator but she has deleted these. Starting with the pp-value, calculate these values of tt and rr.

[5]
c.

Markscheme

H0:ρ=0; H1:ρ>0H0:ρ=0; H1:ρ>0     A1

 

Note:     Do not accept rr in place of ρρ.

 

[1 mark]

a.

insufficient evidence to conclude that there is a (positive) association between marks in these two subjects (or equivalent statement in context)     A1

[1 mark]

b.

degrees of freedom =10=10     (A1)

required value of t=inverse t(0.823)t=inverse t(0.823)     (M1)

=0.972=0.972     A1

attempt to solve t=rn21r2t=rn21r2     (M1)

r=0.294r=0.294     A1

 

Note:     Accept any rr value that rounds to 0.29.

 

Note:     Follow through their tt value to determine rr.

 

[5 marks]

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Topic 7 - Option: Statistics and probability » 7.7

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