| Exam Board | Edexcel |
|---|---|
| Module | S3 (Statistics 3) |
| Year | 2022 |
| Session | June |
| Marks | 10 |
| Paper | Download PDF ↗ |
| Mark scheme | Download PDF ↗ |
| Topic | Hypothesis test of Spearman’s rank correlation coefficien |
| Type | Handle tied ranks |
| Difficulty | Standard +0.3 This is a straightforward application of Spearman's rank correlation with standard procedures: explaining tied ranks treatment (averaging), calculating rs with given data, and performing a hypothesis test using tables. The tied ranks are minimal and the calculations are routine for S3 level, making it slightly easier than average. |
| Spec | 5.08e Spearman rank correlation5.08f Hypothesis test: Spearman rank |
| Player's rank | Televised tournaments won | Total tournaments won |
| 1 | 55 | 135 |
| 2 | 7 | 33 |
| 3 | 5 | 17 |
| 4 | 2 | 14 |
| 5 | 4 | 9 |
| 6 | 2 | 5 |
| 7 | 9 | 36 |
| 8 | 0 | 15 |
| 9 | 3 | 3 |
| 10 | 0 | 13 |
| Answer | Marks | Guidance |
|---|---|---|
| Answer | Mark | Guidance |
| Assign an average rank between the tied ranks | B1 | Must include reference to "average" rank; ignore comments about PMCC; do not allow "add 0.5 to both ranks" |
| Answer | Marks | Guidance |
|---|---|---|
| Answer | Mark | Guidance |
| Ranks for total tournaments: 1 3 4 6 8 9 2 5 10 7 | M1 | Attempt to rank total tournaments (at least four correct); condone reversed ranks |
| \(\sum d^2 = 0+1+1+4+9+9+25+9+1+9 = 68\) | M1 | Finding differences between players rank and tournament ranks and evaluating \(\sum d^2\); may be implied by 68 |
| \(r_s = 1 - \dfrac{6 \times 68}{10(10^2-1)}\) | dM1 | Dependent on 1st M1; using \(1 - \dfrac{6\sum d^2}{10(99)}\) with their \(\sum d^2\); check \(\sum d^2\) if no value shown |
| \(= 0.5878\ldots\) awrt \(0.588\) | A1 | Allow \(\frac{97}{165}\) |
| Answer | Marks | Guidance |
|---|---|---|
| Answer | Mark | Guidance |
| \(H_0: \rho = 0\), \(H_1: \rho > 0\) | B1 | Both hypotheses correct; must be in terms of \(\rho\); must be attached to \(H_0\) and \(H_1\); if \(r_s\) is negative in (b) allow \(H_1: \rho < 0\) |
| Critical Value \(= 0.5636\) or CR \(\ldots 0.5636\) | B1 | If \(r_s\) is negative in (b) allow \(-0.5636\) |
| Reject \(H_0\) or significant or lies in the critical region | dM1 | Dependent on 2nd B1; correct statement consistent with their (b) and CV; no context needed but do not allow contradicting non-contextual comments |
| There is sufficient evidence of a positive correlation between rank and total tournaments won | A1 | Correct conclusion rejecting \(H_0\); must mention rank and total tournaments; NB if \(H_1: \rho < 0\) used, maximum B1B1dM1A0 |
| Answer | Marks | Guidance |
|---|---|---|
| Answer | Mark | Guidance |
| \(2.5\%\) and \(r_s = 0.6485\) or CR \(\ldots 0.6485\) | B1 | For 2.5% and a correct critical value of 0.6485 |
# Question 1:
## Part (a)
| Answer | Mark | Guidance |
|--------|------|----------|
| Assign an average rank between the tied ranks | B1 | Must include reference to "average" rank; ignore comments about PMCC; do not allow "add 0.5 to both ranks" |
## Part (b)
| Answer | Mark | Guidance |
|--------|------|----------|
| Ranks for total tournaments: 1 3 4 6 8 9 2 5 10 7 | M1 | Attempt to rank total tournaments (at least four correct); condone reversed ranks |
| $\sum d^2 = 0+1+1+4+9+9+25+9+1+9 = 68$ | M1 | Finding differences between players rank and tournament ranks and evaluating $\sum d^2$; may be implied by 68 |
| $r_s = 1 - \dfrac{6 \times 68}{10(10^2-1)}$ | dM1 | Dependent on 1st M1; using $1 - \dfrac{6\sum d^2}{10(99)}$ with their $\sum d^2$; check $\sum d^2$ if no value shown |
| $= 0.5878\ldots$ awrt $0.588$ | A1 | Allow $\frac{97}{165}$ |
## Part (c)
| Answer | Mark | Guidance |
|--------|------|----------|
| $H_0: \rho = 0$, $H_1: \rho > 0$ | B1 | Both hypotheses correct; must be in terms of $\rho$; must be attached to $H_0$ and $H_1$; if $r_s$ is negative in (b) allow $H_1: \rho < 0$ |
| Critical Value $= 0.5636$ or CR $\ldots 0.5636$ | B1 | If $r_s$ is negative in (b) allow $-0.5636$ |
| Reject $H_0$ or significant or lies in the critical region | dM1 | Dependent on 2nd B1; correct statement consistent with their (b) and CV; no context needed but do not allow contradicting non-contextual comments |
| There is sufficient evidence of a positive correlation between rank and total tournaments won | A1 | Correct conclusion rejecting $H_0$; must mention **rank** and **total tournaments**; NB if $H_1: \rho < 0$ used, maximum B1B1dM1A0 |
## Part (d)
| Answer | Mark | Guidance |
|--------|------|----------|
| $2.5\%$ and $r_s = 0.6485$ or CR $\ldots 0.6485$ | B1 | For 2.5% and a correct critical value of 0.6485 |
---
\begin{enumerate}
\item The table below shows the number of televised tournaments won and the total number of tournaments won by the top 10 ranked darts players in 2020
\end{enumerate}
\begin{center}
\begin{tabular}{|l|l|l|}
\hline
Player's rank & Televised tournaments won & Total tournaments won \\
\hline
1 & 55 & 135 \\
\hline
2 & 7 & 33 \\
\hline
3 & 5 & 17 \\
\hline
4 & 2 & 14 \\
\hline
5 & 4 & 9 \\
\hline
6 & 2 & 5 \\
\hline
7 & 9 & 36 \\
\hline
8 & 0 & 15 \\
\hline
9 & 3 & 3 \\
\hline
10 & 0 & 13 \\
\hline
\end{tabular}
\end{center}
Michael did not want to calculate Spearman's rank correlation coefficient between player's rank and the rank in televised tournaments won because there would be tied ranks.\\
(a) Explain how Michael could have dealt with these tied ranks.
Given that the largest number of total tournaments won is ranked number 1\\
(b) calculate the value of Spearman's rank correlation coefficient between player's rank and the rank in total tournaments won.\\
(c) Stating your hypotheses and critical value clearly, test at the $5 \%$ level of significance, whether or not there is evidence of a positive correlation between player's rank and the rank in total tournaments won for these darts players.
Michael does not believe that there is a positive correlation between player's rank and the rank in total number of tournaments won.\\
(d) Find the largest level of significance, that is given in the tables provided, which could be used to support Michael's claim.\\
You must state your critical value.
\hfill \mbox{\textit{Edexcel S3 2022 Q1 [10]}}