The United States National Transportation Safety Board was interested in whether, on average, the severity of head injuries sustained in car crashes differed between the sizes of the vehicle driven.The size of vehicle was categorised into four types: Light, Medium, Heavy and Van. 175 randomly chosen vehicles, each containing a crash-test dummy, were driven into a wall at 55 kph and a severity of head injury score was recorded, where the higher the score the more severe the head injury.

Notes :

(i) The data file CrashData.csv is :

(ii) The F?test computer output is below:

ANOVA Head injury Sum of Squares df Mean Square Sig Between Groups 6316986.017 3 1772328.672 8.117 .000 Within Groups 37335777.160 171 218337.878 Total 42652763.177 174 Multiple Comparisons Dependent Variable: Head injury Tukey HSD Mear 95 fidence Interval (1) Vehicle size (J) Vehicle size Difference (I-J) Std. Error Sig. Lower Bound Upper Bound Light Medium 85.943 82. 191 .723 -127.30 299.19 Heavy -11.638 136.332 1.000 -365.35 342.07 Van -417.347 101.335 000 680.26 -154.44 Medium Light 85.943 82. 191 .723 -299.19 127.30 Heavy 97.581 139.140 .896 -458.58 263.41 Van -503.291 105.083 .000 -775.93 -230.66 Heavy Light 11.638 136.332 1.000 -342.07 365.35 Medium 97.581 139.140 .896 -263.41 458.58 Van -405.710 151.240 040 -798.10 -13.32 Van Light 417.347 101.335 000 154.44 680.26 Medium 503.291 105.083 .000 230.66 775.93 Heavy 405.710' 151.240 .040 13.32 798.10 *. The mean difference is significant at the 0.05 level a) For this study describe the: [ 1 mark ]