In a study of reaction times, 25 participants completed a test where their reaction times (in milliseconds) were recorded. The results are shown in the stem-and-leaf diagram below:
20 | 3 5 7 9
21 | 0 2 5 6 8
22 | 1 3 4 5 7 9
23 | 0 2 5 8
24 | 1 4 6 7
25 | 2 5
Key: 21 | 0 represents a reaction time of 210 milliseconds
- State the median reaction time. [1]
- Calculate the interquartile range of these reaction times. [2]
- Find the mean and standard deviation of these reaction times. [3]
- State one advantage of using a stem-and-leaf diagram to display this data rather than a frequency table. [1]
- One participant completed the test again and recorded a reaction time of 195 milliseconds. Add this result to the stem-and-leaf diagram and state the effect this would have on:
a. the median
b. the mean
c. the standard deviation [4]
- Explain why the interquartile range might be preferred to the standard deviation as a measure of spread in this context [2]