ttest
performs t tests on the equality of means. It tests the
hypothesis that a sample has a mean equal to a hypothesized value.
ttest(x, mu = 0, alpha = 0.05, type = c("both", "less", "greater", "all"), ...)
ttest
returns an object of class "ttest"
.
An object of class "ttest"
is a list containing the
following components:
Sheskin, D. J. 2007. Handbook of Parametric and Nonparametric Statistical Procedures, 4th edition. : Chapman & Hall/CRC.
# lower tail ttest(hsb$write, mu = 50, type = 'less')#> One-Sample Statistics #> --------------------------------------------------------------------------------- #> Variable Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] #> --------------------------------------------------------------------------------- #> write 200 52.775 0.6702 9.4786 -Inf 53.8828 #> --------------------------------------------------------------------------------- #> #> Lower Tail Test #> --------------- #> #> Ho: mean(write) >=50 #> Ha: mean(write) <50 #> -------------------------------------------------------------------------------- #> Variable t DF Sig Mean Diff. [95% Conf. Interval] #> -------------------------------------------------------------------------------- #> write 4.141 199 0.99997 2.775 -Inf 3.8828 #> --------------------------------------------------------------------------------# upper tail ttest(hsb$write, mu = 50, type = 'greater')#> One-Sample Statistics #> --------------------------------------------------------------------------------- #> Variable Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] #> --------------------------------------------------------------------------------- #> write 200 52.775 0.6702 9.4786 51.6678 Inf #> --------------------------------------------------------------------------------- #> #> Upper Tail Test #> --------------- #> #> Ho: mean(write) <=50 #> Ha: mean(write) >50 #> -------------------------------------------------------------------------------- #> Variable t DF Sig Mean Diff. [95% Conf. Interval] #> -------------------------------------------------------------------------------- #> write 4.141 199 0.99997 2.775 1.6678 Inf #> --------------------------------------------------------------------------------# both tails ttest(hsb$write, mu = 50, type = 'both')#> One-Sample Statistics #> --------------------------------------------------------------------------------- #> Variable Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] #> --------------------------------------------------------------------------------- #> write 200 52.775 0.6702 9.4786 51.4537 54.0969 #> --------------------------------------------------------------------------------- #> #> Two Tail Test #> --------------- #> #> Ho: mean(write) ~=50 #> Ha: mean(write) !=50 #> -------------------------------------------------------------------------------- #> Variable t DF Sig Mean Diff. [95% Conf. Interval] #> -------------------------------------------------------------------------------- #> write 4.141 199 0.99997 2.775 1.4537 4.0969 #> --------------------------------------------------------------------------------# all tails ttest(hsb$write, mu = 50, type = 'all')#> One-Sample Statistics #> --------------------------------------------------------------------------------- #> Variable Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] #> --------------------------------------------------------------------------------- #> write 200 52.775 0.6702 9.4786 51.4537 54.0969 #> --------------------------------------------------------------------------------- #> #> Ho: mean(write) ~=50 #> #> Ha: mean < 50 Ha: mean ~= 50 Ha: mean > 50 #> t = 4.141 t = 4.141 t = 4.141 #> P < t = 1.0000 P > |t| = 0.0001 P > t = 0.0000