# Chi-squared Watch

1. When performing chi squared statistical test, how do you know what the results you expect are?

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2. You have to assume independence and you multiply the probabilities together and then multiply by the sample size:

P(going to zoo) = 1/10
P(going to park) = 4/10

P(zoo & park) = 0.1 x 0.4 = 0.04 <- Probability that a randomly selected person goes to the park and the zoo, multiply by 10 to get expected value.
3. (Original post by Albino)
You have to assume independence and you multiply the probabilities together and then multiply by the sample size:

P(going to zoo) = 1/10
P(going to park) = 4/10

P(zoo & park) = 0.1 x 0.4 = 0.04 <- Probability that a randomly selected person goes to the park and the zoo, multiply by 10 to get expected value.
So on my example it's birds feeding from different feeders

Feeder A 53 birds
B 43 birds
C 30 birds

How do I approach that?

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4. (Original post by wrnicholls)
So on my example it's birds feeding from different feeders

Feeder A 53 birds
B 43 birds
C 30 birds

How do I approach that?

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Well assuming that the birds are all of the same type, there would only be 1 row/column. which means your expected would be the same as your observed, meaning that chi-squared is 0.
5. Your expected is number of observations/number of categories. So it would be (53+43+30)/3 because there are 3 feeders. It will be the same for a three feeders.
6. (Original post by Tabers)
Your expected is number of observations/number of categories. So it would be (53+43+30)/3 because there are 3 feeders. It will be the same for a three feeders.
Ok so you expect the mean of the values you measure?

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Updated: April 10, 2013
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