OCR S1 2008 January — Question 3 6 marks

Exam BoardOCR
ModuleS1 (Statistics 1)
Year2008
SessionJanuary
Marks6
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicBivariate data
TypeCompare correlation coefficients
DifficultyStandard +0.3 This is a straightforward multi-part question on correlation coefficients requiring standard formula application (part i), conceptual understanding that PMCC of ranks equals Spearman's coefficient (part ii), and knowledge that correlation is scale-invariant (part iii). All parts test recall and basic understanding rather than problem-solving, making it slightly easier than average.
Spec5.08a Pearson correlation: calculate pmcc5.08e Spearman rank correlation

3 A sample of bivariate data was taken and the results were summarised as follows. $$n = 5 \quad \Sigma x = 24 \quad \Sigma x ^ { 2 } = 130 \quad \Sigma y = 39 \quad \Sigma y ^ { 2 } = 361 \quad \Sigma x y = 212$$
  1. Show that the value of the product moment correlation coefficient \(r\) is 0.855 , correct to 3 significant figures.
  2. The ranks of the data were found. One student calculated Spearman's rank correlation coefficient \(r _ { s }\), and found that \(r _ { s } = 0.7\). Another student calculated the product moment coefficient, \(R\), of these ranks. State which one of the following statements is true, and explain your answer briefly.
    (A) \(R = 0.855\) (B) \(R = 0.7\) (C) It is impossible to give the value of \(R\) without carrying out a calculation using the original data.
  3. All the values of \(x\) are now multiplied by a scaling factor of 2 . State the new values of \(r\) and \(r _ { s }\).

3 A sample of bivariate data was taken and the results were summarised as follows.

$$n = 5 \quad \Sigma x = 24 \quad \Sigma x ^ { 2 } = 130 \quad \Sigma y = 39 \quad \Sigma y ^ { 2 } = 361 \quad \Sigma x y = 212$$
\begin{enumerate}[label=(\roman*)]
\item Show that the value of the product moment correlation coefficient $r$ is 0.855 , correct to 3 significant figures.
\item The ranks of the data were found. One student calculated Spearman's rank correlation coefficient $r _ { s }$, and found that $r _ { s } = 0.7$. Another student calculated the product moment coefficient, $R$, of these ranks. State which one of the following statements is true, and explain your answer briefly.\\
(A) $R = 0.855$\\
(B) $R = 0.7$\\
(C) It is impossible to give the value of $R$ without carrying out a calculation using the original data.
\item All the values of $x$ are now multiplied by a scaling factor of 2 . State the new values of $r$ and $r _ { s }$.
\end{enumerate}

\hfill \mbox{\textit{OCR S1 2008 Q3 [6]}}