| Exam Board | OCR MEI |
|---|---|
| Module | Further Statistics A AS (Further Statistics A AS) |
| Year | 2020 |
| Session | November |
| Marks | 12 |
| Paper | Download PDF ↗ |
| Mark scheme | Download PDF ↗ |
| Topic | Chi-squared goodness of fit |
| Type | Spreadsheet-based chi-squared test |
| Difficulty | Standard +0.3 This is a straightforward chi-squared test question requiring students to fill in missing values in a partially completed spreadsheet using standard formulas (expected frequencies = row total × column total / grand total, and contributions = (O-E)²/E). The calculations are routine and the context is clearly structured, making it slightly easier than average for A-level Further Statistics. |
| Spec | 5.06a Chi-squared: contingency tables |
| A | B | C | D | E | F | G | |
| 1 | \multirow{2}{*}{} | Observed frequency | |||||
| 2 | \(\boldsymbol { x } \boldsymbol { \leq } \mathbf { 0 . 3 }\) | \(0.3 < x \leq 0.5\) | \(0.5 < x \leq 0.8\) | x > 0.8 | Totals | ||
| 3 | \multirow[t]{2}{*}{Wears helmet} | Yes | 26 | 27 | 23 | 46 | 122 |
| 4 | No | 45 | 31 | 21 | 31 | 128 | |
| 5 | \multirow{2}{*}{} | Totals | 71 | 58 | 44 | 77 | 250 |
| 6 | |||||||
| 7 | Expected frequency | ||||||
| 8 | \(\boldsymbol { x } \boldsymbol { \leq } \mathbf { 0 . 3 }\) | \(0.3 < x \leq 0.5\) | \(0.5 < x \leq 0.8\) | \(\boldsymbol { x } \boldsymbol { > } \mathbf { 0 . 8 }\) | |||
| 9 | \multirow[t]{2}{*}{Wears helmet} | Yes | 34.6480 | 37.5760 | |||
| 10 | No | 36.3520 | 39.4240 | ||||
| 11 | |||||||
| 12 | \multirow{2}{*}{} | Contribution to the test statistic | |||||
| 13 | \(\boldsymbol { x } \boldsymbol { \leq } \mathbf { 0 . 3 }\) | \(0.3 < x \leq 0.5\) | \(0.5 < x \leq 0.8\) | \(\boldsymbol { x } \boldsymbol { > } \mathbf { 0 . 8 }\) | |||
| 14 | \multirow[t]{2}{*}{Wears helmet} | Yes | 2.1585 | 0.0601 | 0.1087 | 1.8885 | |
| 15 | No | 2.0573 | 0.0573 | 1.8000 | |||
| 16 | |||||||
| Answer | Marks | Guidance |
|---|---|---|
| 6 | (a) | E10: = 22.5280 |
| Answer | Marks |
|---|---|
| = 0.1036 | B1 |
| Answer | Marks |
|---|---|
| [3] | 1.1a |
| Answer | Marks | Guidance |
|---|---|---|
| 1.1 | FT their E10 | |
| 6 | (b) | 22.5280 |
| Answer | Marks |
|---|---|
| curb | B1 |
| Answer | Marks |
|---|---|
| [6] | 3.3 |
| Answer | Marks |
|---|---|
| 3.5a | No further marks if incorrect cv |
| Answer | Marks | Guidance |
|---|---|---|
| 6 | (c) | For distances of 0.3 or below the contributions of |
| Answer | Marks |
|---|---|
| . | E1 |
| Answer | Marks |
|---|---|
| [3] | 2.3 |
| Answer | Marks |
|---|---|
| 3.5a | SC1 if contributions not mentioned but |
Question 6:
6 | (a) | E10: = 22.5280
44×128
E15:
250
2
(21−22.5280)
= 0.1036 | B1
M1
A1
[3] | 1.1a
1.1
1.1 | FT their E10
6 | (b) | 22.5280
H : No association between helmet wearing and
0
distance from curb
H : Some association between helmet wearing and
1
distance from curb
Degrees of freedom = 3
Critical value = 6.251
Test statistic = 2.1585 + 0.0601 + ... + 1.8000 = 8.234
8.234 > 6.251 so reject H
0
There is sufficient evidence to suggest that there is
association between helmet wearing and distance from
curb | B1
B1
B1
B1
M1
A1
[6] | 3.3
3.4
1.1
1.1
2.2b
3.5a | No further marks if incorrect cv
used
M1 for comparison of their ‘8.234’
(using their answer from (a)) with 6.251
leading to a conclusion
A1 for non-assertive conclusion in
context. FT their ‘8.234’
6 | (c) | For distances of 0.3 or below the contributions of
2.1585 and 2.0573 suggest that more do not wear
helmets and fewer do than would be expected.
For distances greater than 0.8 the contributions of
1.8885 and 1.8000 suggest that more do wear helmets
and fewer do not than would be expected.
For distances between 0.3 and 0.8 things are as
expected if there were no association.
. | E1
E1
E1
[3] | 2.3
3.5a
3.5a | SC1 if contributions not mentioned but
comments are otherwise correct for
both ‘distances of 0.3 and below’ and
‘distances greater than 0.8’.
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6 A researcher is investigating whether there is any relationship between whether a cyclist wears a helmet and the distance, $x \mathrm {~m}$, the cyclist is from the kerb (the edge of the road). Data are collected at a particular location for a random sample of 250 cyclists.
The researcher carries out a chi-squared test. Fig. 6 is a screenshot showing part of a spreadsheet used to analyse the data. Some values in the spreadsheet have been deliberately omitted.
\begin{table}[h]
\begin{center}
\begin{tabular}{|l|l|l|l|l|l|l|l|}
\hline
& A & B & C & D & E & F & G \\
\hline
1 & \multicolumn{2}{|c|}{\multirow{2}{*}{}} & \multicolumn{5}{|c|}{Observed frequency} \\
\hline
2 & & & $\boldsymbol { x } \boldsymbol { \leq } \mathbf { 0 . 3 }$ & $0.3 < x \leq 0.5$ & $0.5 < x \leq 0.8$ & x > 0.8 & Totals \\
\hline
3 & \multirow[t]{2}{*}{Wears helmet} & Yes & 26 & 27 & 23 & 46 & 122 \\
\hline
4 & & No & 45 & 31 & 21 & 31 & 128 \\
\hline
5 & \multirow{2}{*}{} & Totals & 71 & 58 & 44 & 77 & 250 \\
\hline
6 & & & & & & & \\
\hline
7 & \multicolumn{2}{|c|}{} & \multicolumn{4}{|c|}{Expected frequency} & \\
\hline
8 & & & $\boldsymbol { x } \boldsymbol { \leq } \mathbf { 0 . 3 }$ & $0.3 < x \leq 0.5$ & $0.5 < x \leq 0.8$ & $\boldsymbol { x } \boldsymbol { > } \mathbf { 0 . 8 }$ & \\
\hline
9 & \multirow[t]{2}{*}{Wears helmet} & Yes & 34.6480 & & & 37.5760 & \\
\hline
10 & & No & 36.3520 & & & 39.4240 & \\
\hline
11 & \multicolumn{2}{|c|}{} & \multicolumn{4}{|c|}{} & \\
\hline
12 & \multirow{2}{*}{} & & \multicolumn{4}{|c|}{Contribution to the test statistic} & \\
\hline
13 & & & $\boldsymbol { x } \boldsymbol { \leq } \mathbf { 0 . 3 }$ & $0.3 < x \leq 0.5$ & $0.5 < x \leq 0.8$ & $\boldsymbol { x } \boldsymbol { > } \mathbf { 0 . 8 }$ & \\
\hline
14 & \multirow[t]{2}{*}{Wears helmet} & Yes & 2.1585 & 0.0601 & 0.1087 & 1.8885 & \\
\hline
15 & & No & 2.0573 & 0.0573 & & 1.8000 & \\
\hline
16 & \multicolumn{7}{|c|}{} \\
\hline
\end{tabular}
\captionsetup{labelformat=empty}
\caption{Fig. 6}
\end{center}
\end{table}
\begin{enumerate}[label=(\alph*)]
\item Showing your calculations, find the missing values in each of the following cells.
\begin{itemize}
\item E10
\item E15
\item In this question you must show detailed reasoning.
\end{itemize}
Carry out a hypothesis test at the $10 \%$ significance level to investigate whether there is any association between helmet wearing and distance from the kerb.
\item Discuss briefly what the data suggest about helmet wearing for different distances from the kerb.
\end{enumerate}
\hfill \mbox{\textit{OCR MEI Further Statistics A AS 2020 Q6 [12]}}