Question 13.9: Gender of Train Passengers On a commuter train, the conducto......

Gender of Train Passengers

On a commuter train, the conductor wishes to see whether the passengers enter the train at random. He observes the first 25 people, with the following sequence of males (M) and females (F).

F F F M M F F F F M F M M M F F F F M M F F F M M

Test for randomness at α = 0.05.

Step-by-Step
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Step 1 State the hypotheses and identify the claim.

H_{0} : The passengers board the train at random, according to gender (claim).

H_{1} : The passengers do not board the train at random, according to gender.

Step 2 Determine the critical value. There are 10 \mathrm{M} ‘s and 15 \mathrm{~F} ‘s, so n_{1}=10 and n_{2}=15. Using Table M and \alpha=0.05, the critical value is { }_{18}^{7} which means do not reject H_{0} if the number of runs is between 7 and 18 .

Step 3 Find the test value. Determine the number of runs. Arrange the letters according to runs of males and females, as shown.

\begin{array}{|c|l|} \hline Run & Gender \\ \hline 1 & F F F \\ 2 & M M \\ 3 & F F F F \\ 4 & M \\ 5 & F \\ 6 & M M M \\ 7 & F F F F \\ 8 & M M \\ 9 & F F F \\ 10 & M M \\ \hline \end{array}

There are 10 runs.

Step 4 Make the decision. Compare these critical values with the number of runs. Since the number of runs is 10 and 10 is between 7 and 18 , do not reject the null hypothesis.

Step 5 Summarize the results. There is not enough evidence to reject the hypothesis that the passengers board the train at random according to gender.

TABLE  M  Critical Values for the Number of Runs
This table gives the critical values at 𝛼 = 0.05 for a two-tailed test. Reject the null hypothesis if the number of runs is less than or equal to the smaller value or greater than or equal to the larger value.
Value of n2
Value of n1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
2 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2
6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6
3 1 1 1 1 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3
6 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8
4 1 1 1 2 2 2 3 3 3 3 3 3 3 3 4 4 4 4 4
6 8 9 9 9 10 10 10 10 10 10 10 10 10 10 10 10 10 10
5 1 1 2 2 3 3 3 3 3 4 4 4 4 4 4 4 5 5 5
6 8 9 10 10 11 11 12 12 12 12 12 12 12 12 12 12 12 12
6 1 2 2 3 3 3 3 4 4 4 4 5 5 5 5 5 5 6 6
6 8 9 10 11 12 12 13 13 13 13 14 14 14 14 14 14 14 14
7 1 2 2 3 3 3 4 4 5 5 5 5 5 6 6 6 6 6 6
6 8 10 11 12 13 13 14 14 14 14 15 15 15 16 16 16 16 16
8 1 2 3 3 3 4 4 5 5 5 6 6 6 6 6 7 7 7 7
6 8 10 11 12 13 14 14 15 15 16 16 16 16 17 17 17 17 17
9 1 2 3 3 4 4 5 5 5 6 6 6 7 7 7 7 8 8 8
6 8 10 12 13 14 14 15 16 16 16 17 17 18 18 18 18 18 18
10 1 2 3 3 4 5 5 5 6 6 7 7 7 7 8 8 8 8 9
6 8 10 12 13 14 15 16 16 17 17 18 18 18 19 19 19 20 20
11 1 2 3 4 4 5 5 6 6 7 7 7 8 8 8 9 9 9 9
6 8 10 12 13 14 15 16 17 17 18 19 19 19 20 20 20 21 21
12 2 2 3 4 4 5 6 6 7 7 7 8 8 8 9 9 9 10 10
6 8 10 12 13 14 16 16 17 18 19 19 20 20 21 21 21 22 22
13 2 2 3 4 5 5 6 6 7 7 8 8 9 9 9 10 10 10 10
6 8 10 12 14 15 16 17 18 19 19 20 20 21 21 22 22 23 23
14 2 2 3 4 14 5 6 7 7 8 8 9 9 9 10 10 10 11 11
6 8 10 12 14 15 16 17 18 19 20 20 21 22 22 23 23 23 24
15 2 3 3 4 5 6 6 7 7 8 8 9 9 10 10 11 11 11 12
6 8 10 12 14 15 16 18 18 19 20 21 22 22 23 23 24 24 25
16 2 3 4 4 5 6 6 7 8 8 9 9 10 10 11 11 11 12 12
6 8 10 12 14 16 17 18 19 20 21 21 22 23 23 24 25 25 25
17 2 3 4 4 5 6 7 7 8 9 9 10 10 11 11 11 12 12 13
6 8 10 12 14 16 17 18 19 20 21 22 23 23 24 25 25 26 26
18 2 3 4 5 5 6 7 8 8 9 9 10 10 11 11 12 12 13 13
6 8 10 12 14 16 17 18 19 20 21 22 23 24 25 25 26 26 27
19 2 3 4 5 6 6 7 8 8 9 10 10 11 11 12 12 13 13 13
6 8 10 12 14 16 17 18 20 21 22 23 23 24 25 26 26 27 27
20 2 3 4 5 6 6 7 8 9 9 10 10 11 12 12 13 13 13 14
6 8 10 12 14 16 17 18 20 21 22 23 24 25 25 26 27 27 28

Source: Adapted from C. Eisenhardt and F. Swed, “Tables for Testing Randomness of Grouping in a Sequence of Alternatives,” The Annals of Statistics, vol. 14 (1943), pp. 83–86. Reprinted with permission of the Institute of Mathematical Statistics and of the Benjamin/Cummings Publishing Company, in whose publication, Elementary Statistics, 3rd ed. (1989), by Mario F. Triola, this table appears.

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