How to calculate chi sqaure value from statistical value and degrees of freedom?

[Manish Gupta]

Hi,

How to calculate chi sqaure p value for given statistical value and degrees of freedom.

Input :
x = statistical value
d = degrees of freedom
output:
p value = ?

Regards

[Özgür Asar]

Hi,

Try

pchisq(q,df)

available at help(Chisquare)

Ozgur

[Manish Gupta]

Hi,

My input is chi square statistical value and degrees of freedom. But i m getting different p values with the above formula.

I double checked my values with the below calculator.

http://vassarstats.net/tabs.html#csq

Pls help me out.  

[Özgür Asar]

Hi,

Actually, pchisq(q,df) calculates the cumulative distribution function by default.

To calculate the p-value, you can use either

1-pchisq(q,df)

or

pchisq(q,df,lower.tail=FALSE)

PS: I checked, the p value yielded by R and the calculator for which you give a link, for some "q" and "df" values, and these two are same.

Best
Ozgur

[Rui Barradas]

Hello,

You are computing the lower tail value, for chi-squared tests it's
probably the upper tail you want.

p.val1 <- 1 - pchisq(Stat, df)
p.val2 <- pchisq(Stat, df, lower.tail=FALSE)
p.val1 == p.val2

Hope this helps,

Rui Barradas

Em 06-06-2012 02:31, Manish Gupta escreveu:

> Hi,
>
> My input is chi square statistical value and degrees of freedom. But i m
> getting different p values with the above formula.
>
> I double checked my values with the below calculator.
>
> http://vassarstats.net/tabs.html#csq
>
> Pls help me out.
>
> --
> View this message in context: http://r.789695.n4.nabble.com/How-to-calculate-chi-sqaure-value-from-statistical-value-and-degrees-of-freedom-tp4632385p4632467.html
> Sent from the R help mailing list archive at Nabble.com.
>
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