statistical significance (p value)?

Hello

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 t-test and the sample size.

E.g.

For t-test of paired samples X (sample size = N, i.e., pair count = N, data count = 2 * N), d.o.f. = N - 1.

For t-test 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

A,

TDIST is used in Excel to calculate p-values, 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 t-distribution.

TDIST(non-neg-x-value, degrees-freedom, tails)

• non-neg-x-value: The value at which you want to evaluate the function. non-neg-x-value is a number value that must be greater than or equal to 0.
• degrees-freedom: Degrees of freedom. degrees-freedom 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 one-tailed distribution.
  • two tails (2): Return the value for a two-tailed distribution.

Jerry

Hello

As far as I know, TTEST() function returns the p-value of the specified t-test.

Regards,

H

You're quite welcome! Glad to be of help.

Best wishes,

Hiroto