| Date | November 2008 | Marks available | 1 | Reference code | 08N.1.sl.TZ0.11 |
| Level | SL only | Paper | 1 | Time zone | TZ0 |
| Command term | Give a reason | Question number | 11 | Adapted from | N/A |
Question
The marks obtained by 8 candidates in Physics and Chemistry tests are given below.
Write down the product moment correlation coefficient, \(r\).
Write down, in the form \(y = mx + c\) , the equation of the regression line \(y\) on \(x\) for the \(8\) candidates.
A ninth candidate obtained a score of \(7\) in the Physics test but was absent for the Chemistry test.
Use your answer to (b) to estimate the score he would have obtained on the Chemistry test.
Give a reason why it is valid to use this regression line to estimate the score on the Chemistry test in part (c).
Markscheme
\(0.965\) (A1) (C1)
[1 mark]
\(y = 1.15x + 0.976\) (A1)(A1) (C2)
Note: (A1) for \(1.15x\). (A1) for \( + 0.976\).
[2 marks]
\(y = 1.15(7) + 0.976\) (M1)
\({\text{Chemistry}} = 9.03\) (accept \(9\)) (A1)(ft) (C2)
Note: Follow through from candidate's answer to (b) even if no working is seen. Award (A2)(ft).
[2 marks]
the correlation coefficient is close to \(1\)
OR strongly correlated variables
OR \(7\) lies within the range of physics marks. (R1) (C1)
[1 mark]
Examiners report
The level of accuracy required by the paper was often ignored in this question.
(a) Some candidates are unable to recover \(r\) from a reset calculator.
The level of accuracy required by the paper was often ignored in this question.
The level of accuracy required by the paper was often ignored in this question.
(c) Many candidates seem to be unaware when it is appropriate to use a regression line.
The level of accuracy required by the paper was often ignored in this question.
