ifr_ts_ind_ttest compares the means of two independent groups in order to determine whether
there is statistical evidence that the associated population means are significantly different.
Usage
ifr_ts_ind_ttest(
data,
x,
y,
confint = 0.95,
alternative = c("both", "less", "greater", "all"),
...
)Arguments
- data
a data frame
- x
factor; a column in
data- y
numeric; a column in
data- confint
confidence level
- alternative
a character string specifying the alternative hypothesis, must be one of "both" (default), "greater", "less" or "all". You can specify just the initial letter
- ...
additional arguments passed to or from other methods
Value
ifr_ts_ind_ttest returns an object of class "ifr_ts_ind_ttest".
An object of class "ifr_ts_ind_ttest" is a list containing the
following components:
- levels
levels of
x- obs
number of observations of
yfor each level ofx- n
total number of observations
- mean
mean of
yfor each level ofx- sd
standard deviation of
yfor each level ofx- se
estimate of standard error of
yfor each level ofx- lower
lower limit for the mean of
yfor each level ofx- upper
upper limit for the mean of
yfor each level ofx- combined
a data frame; mean, standard deviation, standard error and confidence limit of mean of
y- mean_diff
difference in mean of
yfor the two groups ofx- se_dif
estimate of the standard error for difference in mean of
yfor the two groups ofx- sd_dif
degrees of freedom
- conf_diff
confidence interval for
mean_diff- df_pooled
degrees of freedom for the pooled method
- df_satterthwaite
degrees of freedom for the Satterthwaite method
- t_pooled
t statistic for the pooled method
- t_satterthwaite
t statistic for the Satterthwaite method
- sig_pooled
two-sided p-value for the pooled method
- sig_pooled_l
lower one-sided p-value for the pooled method
- sig_pooled_u
upper one-sided p-value for the pooled method
- sig
two-sided p-value for the Satterthwaite method
- sig_l
lower one-sided p-value for the Satterthwaite method
- sig_u
upper one-sided p-value for the Satterthwaite method
- num_df
numerator degrees of freedom for folded f test
- den_df
denominator degrees of freedom for folded f test
- f
f value for the equality of variances test
- f_sig
p-value for the folded f test
- var_y
name of
y- confint
confidence level
- alternative
alternative hypothesis
References
Sheskin, D. J. 2007. Handbook of Parametric and Nonparametric Statistical Procedures, 4th edition. : Chapman & Hall/CRC.
Examples
# lower tail
ifr_ts_ind_ttest(hsb, female, write, alternative = 'less')
#> Group Statistics
#> -----------------------------------------------------------------------------
#> Group Obs Mean Std. Err. Std. Dev. [95% Conf. Interval]
#> -----------------------------------------------------------------------------
#> 0 91 50.121 1.080 10.305 47.97539 52.26661
#> 1 109 54.991 0.779 8.134 53.44689 56.53511
#> -----------------------------------------------------------------------------
#> combined 200 52.775 0.67 9.479 51.45379 54.09621
#> -----------------------------------------------------------------------------
#> diff 200 -4.87 1.304 9.231 -7.42623 -2.31377
#> -----------------------------------------------------------------------------
#>
#> Independent Samples Test
#> ------------------------
#>
#> Ho: mean(0) - mean(1) = diff = 0
#> Ha: diff < 0
#>
#> ---------------------------------------------------------------------
#> Variable Method Variances DF t Value P < t
#> ---------------------------------------------------------------------
#> write Pooled Equal 198 -3.7341 0.0001
#> write Satterthwaite Unequal 170 -3.6564 0.0002
#> ---------------------------------------------------------------------
#>
#> Test for Equality of Variances
#> ---------------------------------------------------------------
#> Variable Method Num DF Den DF F Value P > F
#> ---------------------------------------------------------------
#> write Folded F 90 108 1.605 0.0188
#> ---------------------------------------------------------------
# upper tail
ifr_ts_ind_ttest(hsb, female, write, alternative = 'greater')
#> Group Statistics
#> -----------------------------------------------------------------------------
#> Group Obs Mean Std. Err. Std. Dev. [95% Conf. Interval]
#> -----------------------------------------------------------------------------
#> 0 91 50.121 1.080 10.305 47.97539 52.26661
#> 1 109 54.991 0.779 8.134 53.44689 56.53511
#> -----------------------------------------------------------------------------
#> combined 200 52.775 0.67 9.479 51.45379 54.09621
#> -----------------------------------------------------------------------------
#> diff 200 -4.87 1.304 9.231 -7.42623 -2.31377
#> -----------------------------------------------------------------------------
#>
#> Independent Samples Test
#> ------------------------
#>
#> Ho: mean(0) - mean(1) = diff = 0
#> Ha: diff > 0
#>
#> ---------------------------------------------------------------------
#> Variable Method Variances DF t Value P > t
#> ---------------------------------------------------------------------
#> write Pooled Equal 198 -3.7341 0.9999
#> write Satterthwaite Unequal 170 -3.6564 0.9998
#> ---------------------------------------------------------------------
#>
#> Test for Equality of Variances
#> ---------------------------------------------------------------
#> Variable Method Num DF Den DF F Value P > F
#> ---------------------------------------------------------------
#> write Folded F 90 108 1.605 0.0188
#> ---------------------------------------------------------------
# both tails
ifr_ts_ind_ttest(hsb, female, write, alternative = 'both')
#> Group Statistics
#> -----------------------------------------------------------------------------
#> Group Obs Mean Std. Err. Std. Dev. [95% Conf. Interval]
#> -----------------------------------------------------------------------------
#> 0 91 50.121 1.080 10.305 47.97539 52.26661
#> 1 109 54.991 0.779 8.134 53.44689 56.53511
#> -----------------------------------------------------------------------------
#> combined 200 52.775 0.67 9.479 51.45379 54.09621
#> -----------------------------------------------------------------------------
#> diff 200 -4.87 1.304 9.231 -7.42623 -2.31377
#> -----------------------------------------------------------------------------
#>
#> Independent Samples Test
#> ------------------------
#>
#> Ho: mean(0) - mean(1) = diff = 0
#> Ha: diff ~= 0
#>
#> ---------------------------------------------------------------------
#> Variable Method Variances DF t Value P > |t|
#> ---------------------------------------------------------------------
#> write Pooled Equal 198 -3.7341 0.0002
#> write Satterthwaite Unequal 170 -3.6564 0.0003
#> ---------------------------------------------------------------------
#>
#> Test for Equality of Variances
#> ---------------------------------------------------------------
#> Variable Method Num DF Den DF F Value P > F
#> ---------------------------------------------------------------
#> write Folded F 90 108 1.605 0.0188
#> ---------------------------------------------------------------
# all tails
ifr_ts_ind_ttest(hsb, female, write, alternative = 'all')
#> Group Statistics
#> -----------------------------------------------------------------------------
#> Group Obs Mean Std. Err. Std. Dev. [95% Conf. Interval]
#> -----------------------------------------------------------------------------
#> 0 91 50.121 1.080 10.305 47.97539 52.26661
#> 1 109 54.991 0.779 8.134 53.44689 56.53511
#> -----------------------------------------------------------------------------
#> combined 200 52.775 0.67 9.479 51.45379 54.09621
#> -----------------------------------------------------------------------------
#> diff 200 -4.87 1.304 9.231 -7.42623 -2.31377
#> -----------------------------------------------------------------------------
#>
#> Independent Samples Test
#> ------------------------
#>
#> Ho: mean(0) - mean(1) = diff = 0
#>
#> Ha: diff < 0 Ha: diff ~= 0 Ha: diff > 0
#>
#> Pooled
#> ------------------------------------------------------------------------
#> t = -3.7341 t = -3.7341 t = -3.7341
#> P < t = 0.0001 P > |t| = 0.0002 P > t = 0.9999
#>
#> Satterthwaite
#> ------------------------------------------------------------------------
#> t = -3.6564 t = -3.6564 t = -3.6564
#> P < t = 0.0002 P > |t| = 0.0003 P > t = 0.9998
#>
#>
#> Test for Equality of Variances
#> ---------------------------------------------------------------
#> Variable Method Num DF Den DF F Value P > F
#> ---------------------------------------------------------------
#> write Folded F 90 108 1.605 0.0188
#> ---------------------------------------------------------------