In: Statistics and Probability
A traffic safety company publishes reports about motorcycle fatalities and helmet use. In the first accompanying data table, the distribution shows the proportion of fatalities by location of injury for motorcycle accidents. The second data table shows the location of injury and fatalities for 2068 riders not wearing a helmet.
Location of Injury Probability
Frequency
Multiple Locations 0.570 1027
Head 0.310 869
Neck 0.030 40
Thorax 0.060 83
Abdomen/Lumbar/Spine 0.030 49
(a) Does the distribution of fatal injuries for riders not wearing a helmet follow the distribution for all riders? Use
alphaαequals=0.050.05
level of significance. What are the null and alternative hypotheses?
A.
H0: The distribution of fatal injuries for riders not wearing a helmet does not follow the same distribution for all other riders.
H1: The distribution of fatal injuries for riders not wearing a helmet does follow the same distribution for all other riders.
B.
H0: The distribution of fatal injuries for riders not wearing a helmet follows the same distribution for all other riders.
H1: The distribution of fatal injuries for riders not wearing a helmet does not follow the same distribution for all other riders. Your answer is correct.
C.
None of these.
Compute the expected counts for each fatal injury.
Location of injury |
Observed Count |
Expected Count |
---|---|---|
Multiple Locations |
1027 |
__?__ |
Head |
869 |
__?__ |
Neck |
40 |
__?__ |
Thorax |
83 |
__?__ |
Abdomen/Lumbar/Spine |
49 |
__?__ |
(Round to two decimal places as needed.)
a)
The null and alternative hypothesis is
B.
H0: The distribution of fatal injuries for riders not wearing a helmet follows the same distribution for all other riders.
H1: The distribution of fatal injuries for riders not wearing a helmet does not follow the same distribution for all other riders.
Level of significance = 0.05
Expected count = n*pi
n = 2068
Location of injury | Observed Count | Expected Count |
Multiple Locations | 1027 | 1178.76 |
Head | 869 | 641.08 |
Neck | 40 | 62.04 |
Thorax | 83 | 124.08 |
Abdomen/Lumbar/Spine | 49 | 62.04 |
Test statistic is
O: Observed frequency
E: Expected frequency.
O | p | E | (O-E) | (O-E)^2 | (O-E)^2/E | |
1027 | 0.57 | 1178.76 | -151.76 | 23031.1 | 19.53841 | |
869 | 0.31 | 641.08 | 227.92 | 51947.53 | 81.03127 | |
40 | 0.03 | 62.04 | -22.04 | 485.7616 | 7.829813 | |
83 | 0.06 | 124.08 | -41.08 | 1687.566 | 13.60063 | |
49 | 0.03 | 62.04 | -13.04 | 170.0416 | 2.740838 | |
Total | 2068 | Total | 124.741 |
Degrees of freedom = Number of E's - 1 = 5 - 1 = 4
Critical value = 9.488
( From chi-square critical value table)
Test statistic > critical value we reject null hypothesis.
Conclusion: The distribution of fatal injuries for riders not wearing a helmet does not follow the same distribution for all other riders.