
Jerrold Green1 Jan 24, 2013 9:33 AM
Re: statistical significance (p value)? in response to AxxlbA,
TDIST is used in Excel to calculate pvalues, and the same function is included in Numbers. Use the Function Browser to review the syntax for the function:
The TDIST function returns the probability from the student’s tdistribution.
 TDIST(nonnegxvalue, degreesfreedom, tails)
 nonnegxvalue: The value at which you want to evaluate the function. nonnegxvalue is a number value that must be greater than or equal to 0.
 degreesfreedom: Degrees of freedom. degreesfreedom is a number value and must be greater than or equal to 1.
 tails: The number of tails to return.
 one tail (1): Return the value for a onetailed distribution.
 two tails (2): Return the value for a twotailed distribution.
Jerry
 TDIST(nonnegxvalue, degreesfreedom, tails)

Hiroto Jan 24, 2013 11:19 AM
Re: statistical significance (p value)? in response to AxxlbHello
As far as I know, TTEST() function returns the pvalue of the specified ttest.
Regards,
H

Axxlb Jan 24, 2013 12:32 PM
Re: statistical significance (p value)? in response to Jerrold Green1jerrold,
thank you very much, it seems working with TDIST, which in french is LOI.STUDENT
thanks a lot!
hiroto,
isn't that the t value with ttest only?

Axxlb Jan 24, 2013 1:56 PM
Re: statistical significance (p value)? in response to Hirotoactually, the ttest function might return the pvalue. in that case, how can I have my t value???
thanks

Hiroto Jan 25, 2013 2:06 PM
Re: statistical significance (p value)? in response to AxxlbHello
The maps between t value and p value are provided by TINV() and TDIST().
t value = TINV(p value, degrees of freedom) p value = TDIST(t value, degrees of freedom, number of tails)
The t distribution is determined by the degrees of freedom (d.o.f.) of the t statistic in use and the d.o.f. is determined by the type of ttest and the sample size.
E.g.
For ttest of paired samples X (sample size = N, i.e., pair count = N, data count = 2 * N), d.o.f. = N  1.
For ttest of two independent samples X1, X2 assumed to have equal population variance (sample size = N1, N2 resp.), d.o.f. = N1 + N2  2.
If you want t value, you may a) use t = TINV(TTEST(), d.o.f.) or b) calculate it directly from sample data without using TTEST() function.
E.g.,
p = TTEST(samples_1, samples_2, 2, 2)
is equivalent to 
X1 = samples_1 X2 = samples_2 N1 = COUNT(X1) N2 = COUNT(X2) PV = (VAR(X1) * (N1  1) + VAR(X2) * (N2  1)) / (N1 + N2  2) t = (SUM(X1) / N1  SUM(X2) / N2) / SQRT(PV * (1 / N1 + 1 / N2)) p = TDIST( ABS(t), N1 + N2  2, 2)
*PV is pooled variance.
Hope this helps,
H

Axxlb Jan 28, 2013 6:28 AM
Re: statistical significance (p value)? in response to Hirotocool, I think I got it, thank you very much !
then, i'm using the TINV and the TTEST functions
thanks again!

Hiroto Jan 28, 2013 7:05 AM
Re: statistical significance (p value)? in response to AxxlbYou're quite welcome! Glad to be of help.
Best wishes,
Hiroto