In: Statistics and Probability
In 1912 the luxury liner Titanic on its first voyage across the Atlantic, struck an iceberg and sank. Some passengers got off the ship in lifeboats, but many died. Think of the Titanic disaster as an experiment in how the people of that time behaved when faced with death in a situation where only some can escape. The passengers are a sample from the population of their peers. Here is a table showing who survived the sinking of the Titanic based on whether they were crew members, or passengers booked in first-, second-, or third-class staterooms:
crew | First | Second | Third | Total | |
Alive Dead |
212 |
202 123 |
118 167 |
178 528 |
710 1491 |
Total | 885 | 325 | 285 | 706 | 2201 |
. Calculate the survival rates (the number who survived divided by the number in the group) for each of the four groups. b. (1 mark) Write null and alternative hypotheses to assess whether group and survival are related. c. Is there strong evidence that the survival rates are not all the same? If not, what differences seem important?
a)
crew | first | second | third | |
survival rate= | 24.0% | 62.2% | 41.4% | 25.2% |
b)
Ho: group and survival are related
H1: group and survival are not related
c)
Chi-Square Test of independence | |||||||
Observed Frequencies | |||||||
crew | first | second | third | Total | |||
alive | 212 | 202 | 118 | 178 | 710 | ||
dead | 673 | 123 | 167 | 528 | 1491 | ||
Total | 885 | 325 | 285 | 706 | 2201 | ||
Expected frequency of a cell = sum of row*sum of column / total sum | |||||||
Expected Frequencies | |||||||
crew | first | second | third | Total | |||
alive | 885*710/2201=285.484 | 325*710/2201=104.839 | 285*710/2201=91.935 | 706*710/2201=227.742 | 710 | ||
dead | 885*1491/2201=599.516 | 325*1491/2201=220.161 | 285*1491/2201=193.065 | 706*1491/2201=478.258 | 1491 | ||
Total | 885 | 325 | 285 | 706 | 2201 | ||
(fo-fe)^2/fe | |||||||
alive | 18.9148 | 90.0461 | 7.390 | 10.864 | |||
dead | 9.0071 | 42.8791 | 3.519 | 5.173 |
Chi-Square Test Statistic,χ² = Σ(fo-fe)^2/fe
= 187.7932
Level of Significance = 0.05
Number of Rows = 2
Number of Columns = 4
Degrees of Freedom=(#row - 1)(#column -1) = (2- 1 ) * ( 4- 1 )
= 3
p-Value = 0.0000 [Excel function:
=CHISQ.DIST.RT(χ²,df) ]
Decision: p-value < α , Reject Ho
There is strong evidence that the survival rates are not all the same
in group first class, survival rate is highest