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# What does "fit a poisson distribution" mean? watch

1. My question is:

"Fit a Poisson distribution to the following frequency distribution and test the goodness of ft. State clearly the hypothesis being tested and the conclusion which is reached".

After looking online, I found out the hypothesis would simply be H(o) - The following data fit's a Poisson distrubution, and H(1) - The data doesn't.

I think that is correct as the question is all the data we have been given.

However I don't understand what is meant by "Fit a Poisson distribution" and when testing the goodness of fit, how would I work out the expected values as our table as 2 rows, one for 'x' and one for the frequency, and again, the question is the whole question we have been given, there are no other parts to it.

Thank you
2. Right. That is correct that the null hypothesis is that the variable and the data fits a Poisson distribution. To calucate the expected values, you just calcuate the probability of the event (eg : P(x=2)) and you multiply that by the total observed frequencies. You know then you have to find the {(Observed frequency - Expected frequency)^2}/{Expected frequency}, to caluclate the Chi-squared value
3. (Original post by CookieGhoul)
Right. That is correct that the null hypothesis is that the variable and the data fits a Poisson distribution. To calucate the expected values, you just calcuate the probability of the event (eg : P(x=2)) and you multiply that by the total observed frequencies. You know then you have to find the {(Observed frequency - Expected frequency)^2}/{Expected frequency}, to caluclate the Chi-squared value
Then when I do this chi squared bit, what am I looking for?
4. Nothing. Just compare it with the value in the formula booklet with the appropriate level of significance. I assume that you know how to do this ?
5. (Original post by CookieGhoul)
Nothing. Just compare it with the value in the formula booklet with the appropriate level of significance. I assume that you know how to do this ?
Oh and do a normal hypotheses test thing with it? Cool, thanks

Just one more question, my very first one lol. What does "fit a poission distribution" mean? Is it simply drawing the Poisson distribution?
6. (Original post by claret_n_blue)
Oh and do a normal hypotheses test thing with it? Cool, thanks

Just one more question, my very first one lol. What does "fit a poission distribution" mean? Is it simply drawing the Poisson distribution?
Lol no. Your not drawing it. When they say "fit", they mean whether or not the data corresponds to a variable that follows a poisson distribution. Your expected values are then calulated using the probability formulas for the Poisson distribution
7. (Original post by CookieGhoul)
Lol no. Your not drawing it. When they say "fit", they mean whether or not the data corresponds to a variable that follows a poisson distribution. Your expected values are then calulated using the probability formulas for the Poisson distribution
So the whole point of them mentioning Poission is to tell me what formula/tables I have to use to work out the expected values. If they said fit a Binomial, would I do the same thing but using the binomial formula instead?
8. (Original post by claret_n_blue)
So the whole point of them mentioning Poission is to tell me what formula/tables I have to use to work out the expected values. If they said fit a Binomial, would I do the same thing but using the binomial formula instead?
Exactly

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