A survey found that of the 320 people questioned who had passed their driving test aged under twenty-five, 104 had been involved in an accident in the two years following their test. Of the 80 people in the survey who were aged twenty-five or over when they passed their test, 16 had been involved in an accident in the following two years.
- Draw up a contingency table showing this information. [2]
It is desired to test whether the proportion of drivers having accidents within two years of passing their test is different for those who were aged under twenty-five at the time of passing their test than for those aged twenty-five or over.
- Stating your hypotheses clearly, carry out the test at the 5\% level of significance.
- Explain clearly why there is only one degree of freedom. [11]
It is found that 12 people who were aged under twenty-five when they took their test and had been involved in an accident in the following two years had been omitted from the information given.
- Explain why you do not need to repeat the calculation to know the correct result of the test. [2]