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In many cities, neighborhood Crime Watch groups are formed in an attempt to reduce the amount of criminal activity. Suppose one neighborhood that has experienced an average of 10 crimes per year organizes a Crime Watch group. During the first year following the creation of the group, 3 crimes are committed in the neighborhood

Use the Poisson distribution to calculate the probability the 3 or fewer crimes are committed in a year, assuming that the average number is still 10 times per year

Average = 10 x = 3 Answer would be P(X < 3) = 0.00277?

Do you think this event provides some evidence that the Crime watch group has been effective in this neighborhood? Justify your answer below. Im lost at this one, any help would be appreciated.

kjetil b halvorsen
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user3236592
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  • OK, but, for self-study questions you need to show what work you have done, what you have tried and where, specifically, you are stuck. – Peter Flom Apr 06 '14 at 15:08
  • @PeterFlom, edited, please advise – user3236592 Apr 06 '14 at 15:20
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    Although your answer likely was the one intended, in fact *the information given is insufficient to support a definite answer.* The average of $10$ is itself an estimate, subject to uncertainty. It is not appropriate to assume $10$ is the true rate. An appropriate test would account for that uncertainty. For instance, suppose "10 crimes per year" summarizes only the previous year's experience. Now the (two-sided) p-value is $9\%$, which is scarcely significant evidence of a change. This exemplifies how textbook ("self-study") questions differ from *real* questions in statistics. – whuber Jan 04 '17 at 17:26

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