In: Statistics and Probability
Use a 5% significance level.
In a large city, 200 persons were selected at random and each person was asked how many tickets he purchased that week in the state lottery. The results are given in the following table. Suppose that among the 7 persons who had purchased five or more tickets, 3 persons had purchased exactly five tickets, 2 persons had purchased six tickets, 1 had purchased seven tickets, and 1 had purchased ten tickets. Test the hypothesis that these 200 observations form a random sample from a Poisson distribution.
Number of tickets previously purchased | Number of Persons |
0 | 52 |
1 | 60 |
2 | 55 |
3 | 18 |
4 | 8 |
5 or more | 7 |
ANSWER::
Ho: distribution is poisson probability distribution
Ha: distribution is not the poisson probability distribution
total observation = ΣO =200
µ = ΣX*O/n = 291/200=1.455
expected proportion = e-µ * µ^x / x!
expected frequency = expected proportion * total
observation
X | observed (O)=f | X*O | expected proportion,p = e-µ * µ^x / x! | expected frequency ( E )=p*ΣO |
0 | 52 | 0 | 0.233 | 46.680 |
1 | 60 | 60 | 0.340 | 67.920 |
2 | 55 | 110 | 0.247 | 49.411 |
3 | 18 | 54 | 0.120 | 23.965 |
4 | 8 | 32 | 0.044 | 8.717 |
5 or more | 7 | 35 | 0.017 | 3.307 |
expecte dfrequency is less than 5, so we will merge last two rows.
X | observed (O)=f | X*O | expected proportion,p = e-µ * µ^x / x! | expected frequency ( E )=p*ΣO | (O-E)²/E |
0 | 52 | 0 | 0.233 | 46.680 | 0.606 |
1 | 60 | 60 | 0.340 | 67.920 | 0.923 |
2 | 55 | 110 | 0.247 | 49.411 | 0.632 |
3 | 18 | 54 | 0.120 | 23.965 | 1.485 |
4 or more | 15 | 60 | 0.060 | 12.024 | 0.736 |
chi square test statistic,X² = Σ(O-E)²/E =
4.383
level of significance, α= 0.05
Degree of freedom=k-2 = 5 -
2 = 3
P value = 0.2230 [ excel function:
=chisq.dist.rt(test-stat,df) ]
Decision: P value >α , Do not reject Ho
conclusion:distribution is poisson probability distribution
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