This function displays d and non-central confidence interval for d for single t tests estimated from the t-statistic.

The formula for d is: $$d = \frac{t}{\sqrt(N)}$$

The formula for t is: $$t = \frac{M - \mu}{SE}$$

R Function

d.single.t.t(t, n, a = 0.05)


  • t = t-test value
  • n = sample size
  • a = significance level


A school has a gifted/honors program that they claim is significantly better than others in the country. The gifted/honors students in this school scored an average of 1370 on the SAT, while the national average for gifted programs is a SAT score of 1080. The data are available on GitHub. Example output from JASP, SPSS, and SAS are shown below.

JASP Single t JASP

SPSS Single t SPSS SAS Single t SAS

Function in R:

d.single.t.t(t = 9.968, n = 15, a = .05)



Single Sample t - t Screenshot

Effect Size:

d = 2.57, 95% CI [1.49, 3.63]


Your confidence interval does not include zero, and therefore, you might conclude that this effect size is different from zero.

Summary Statistics:

Not applicable.

Test Statistic:

t(14) = 9.97, p < .001


Your p-value is less than the alpha value, and therefore, this test would be considered statistically significant.