chi squared - last ever thread

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emmz
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#1
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hi im doing a2 cw and it says on the mark scheme somethig about mentioning critical value. im doing chi squared and my observed value is 75.3 and on the chart it says 0.001. im using df2.
however im not sure wot these facts mean as im crap at maths lol.
cud some1 explain wot they are and tell me wot critical value is
cheers
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txt_eva
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AHHHHHHHHHHHHHHHHHHHHH!!! *Hissss* EBIL!!!

Sorry the chi squares drive me mad!!! It means, I think thats its a probality of 1% of it being wrong... ie that is good
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Sam2k
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(Original post by emmz)
hi im doing a2 cw and it says on the mark scheme somethig about mentioning critical value. im doing chi squared and my observed value is 75.3 and on the chart it says 0.001. im using df2.
however im not sure wot these facts mean as im crap at maths lol.
cud some1 explain wot they are and tell me wot critical value is
cheers
Critical value is number of things comparing minus one
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theone
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(Original post by moncal)
Critical value is number of things comparing minus one
No, that's the number of degrees of freedom, and you need to know a bit more about what you're doing before you can say 'it's -1', you need to know if you've 'guessed' any parameters. The critical value is the value which determines the critical range, i.e. the range in which, if your value of the sum of differences/expected values, lies in, then you reject the null hypothesis.

Sorry if that's a bit too complicated, i've been doing S3 coursework all day
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emmz
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(Original post by theone)
No, that's the number of degrees of freedom, and you need to know a bit more about what you're doing before you can say 'it's -1', you need to know if you've 'guessed' any parameters. The critical value is the value which determines the critical range, i.e. the range in which, if your value of the sum of differences/expected values, lies in, then you reject the null hypothesis.

Sorry if that's a bit too complicated, i've been doing S3 coursework all day
so wot wud my critical value be :confused:
ive only got a hypothesis
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theone
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(Original post by emmz)
so wot wud my critical value be :confused:
ive only got a hypothesis
Well, I don't really know, what's your hypothesis? what does df2 mean? What have you done so far? And by your observed values being 75.3 do you mean the sum of (O-E)^2/E = 75.3?

What is your significance level as well?
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Sam2k
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(Original post by theone)
No, that's the number of degrees of freedom, and you need to know a bit more about what you're doing before you can say 'it's -1', you need to know if you've 'guessed' any parameters. The critical value is the value which determines the critical range, i.e. the range in which, if your value of the sum of differences/expected values, lies in, then you reject the null hypothesis.

Sorry if that's a bit too complicated, i've been doing S3 coursework all day

Thanks for correcting me. My tenth grade biology teacher was a maniac college professor and not a very good teacher.
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theone
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(Original post by moncal)
Thanks for correcting me. My tenth grade biology teacher was a maniac college professor and not a very good teacher.
Oh no problem, apologies if i came across arrogant at all...
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emmz
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(Original post by theone)
Well, I don't really know, what's your hypothesis? what does df2 mean? What have you done so far? And by your observed values being 75.3 do you mean the sum of (O-E)^2/E = 75.3?

What is your significance level as well?
my observed value is 75.3 its wot i got frm the chi squared. ive looked this up on the chart and it says 0.001.
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theone
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(Original post by emmz)
my observed value is 75.3 its wot i got frm the chi squared. ive looked this up on the chart and it says 0.001.
Okay, you're going to have to give me a few more details

What do you mean by 'your observed value'? What have you looked up on the chi-squared chart? Do you know how many degrees of freedom you have? If you don't, then you can't look anything up on the chart? What have you looked up on the chart?
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emmz
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(Original post by theone)
Okay, you're going to have to give me a few more details

What do you mean by 'your observed value'? What have you looked up on the chi-squared chart? Do you know how many degrees of freedom you have? If you don't, then you can't look anything up on the chart? What have you looked up on the chart?
thanx for helping ok ive calculated chi squared and ive got 75.3. my degrees of freedom is 2 (df2) ive looked on the chart along df2 and 75.3 appears under 0.001. so my result from the chart is 0.001.
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