| Date | November 2013 | Marks available | 2 | Reference code | 13N.3sp.hl.TZ0.3 |
| Level | HL only | Paper | Paper 3 Statistics and probability | Time zone | TZ0 |
| Command term | Explain | Question number | 3 | Adapted from | N/A |
Question
Jenny tosses seven coins simultaneously and counts the number of tails obtained. She repeats the experiment 750 times. The following frequency table shows her results.
Explain what can be done with this data to decrease the probability of making a type I error.
(i) State the meaning of a type II error.
(ii) Write down how to proceed if it is required to decrease the probability of making both a type I and type II error.
Markscheme
reduce the significance level (or equivalent statement) R2
[2 marks]
(i) accepting \({{\text{H}}_0}\) (or failing to reject \({{\text{H}}_0}\)) when it is false (or equivalent) A1
(ii) increase the number of trials A1
[2 marks]
Examiners report
It was disappointing to see that some candidates wrote incorrect hypotheses, eg ‘\({{\text{H}}_0}\): Data are binomial; \({{\text{H}}_1}\): Data are not binomial’ without specifying any parameters. Part (b) caused unexpected problems for many candidates who misunderstood the question and gave ‘increase the number of trials’ as their answer.
