Syntax
T.INV.2T(probability, deg_freedom)
| Parameter | Description |
|---|---|
| probability | Parameter of the T.INV.2T function. |
| deg_freedom | Parameter of the T.INV.2T function. |
Examples
Critical value for 95% CI
Formula
=T.INV.2T(0.05, 24)
Returns ~2.0639. Use +/- this value with your sample mean and standard error to construct a 95% confidence interval with 24 df.
Critical value for 99% CI
Formula
=T.INV.2T(0.01, 50)
Returns ~2.6778. The critical t-value for a 99% confidence interval with 50 degrees of freedom.
Small sample critical value
Formula
=T.INV.2T(0.05, 5)
Returns ~2.5706. With only 5 df (n=6), the critical value is much larger than the normal z-value of 1.96, reflecting greater uncertainty.
Common Errors
#NUM!
Probability must be between 0 and 1 (exclusive). Degrees of freedom must be at least 1. Note: the probability here is alpha (e.g., 0.05), not the confidence level.
#VALUE!
Occurs when arguments are non-numeric.
Tips
Alpha, not confidence level
Pass the significance level (alpha), not the confidence level. For a 95% CI, use 0.05, not 0.95. This is the combined probability in both tails.
Always returns positive
T.INV.2T always returns a positive t-value. The critical region is +/- this value. This makes it the natural choice for confidence interval construction.
Confidence interval formula
CI = sample_mean +/- T.INV.2T(alpha, n-1) * (sample_std / SQRT(n)). This is the standard formula for a t-based confidence interval.
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