Two Sample Variance Comparison Test

ifr_ts_var_test performs tests on the equality of standard deviations (variances).

Usage

ifr_ts_var_test(
  data,
  ...,
  group_var = NULL,
  alternative = c("less", "greater", "all")
)

Arguments

data

a data.frame or tibble

...

numeric; column(s) in data

group_var

factor; column in data

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.

Value

ifr_ts_var_test returns an object of class "ifr_ts_var_test". An object of class "ifr_ts_var_test" is a list containing the following components:

f

f statistic

lower

lower one-sided p-value

upper

upper one-sided p-value

two_tail

two-sided p-value

vars

variances for each level of the grouping variable

avgs

means for each level of the grouping variable

sds

standard deviations for each level of the grouping variable

ses

standard errors for each level of the grouping variable

avg

combined mean

sd

combined standard deviation

se

estimated combined standard error

n1

numerator degrees of freedom

n2

denominator degrees of freedom

lens

number of observations for each level of grouping variable

len

number of observations

lev

levels of the grouping variable

type

alternative hypothesis

Deprecated Function

infer_ts_var_test() has been deprecated. Instead use ifr_ts_var_test().

References

Sheskin, D. J. 2007. Handbook of Parametric and Nonparametric Statistical Procedures, 4th edition. : Chapman & Hall/CRC.

See also

var.test

Examples

# using grouping variable
ifr_ts_var_test(hsb, read, group_var = female, alternative = 'less')
#>                Variance Ratio Test                 
#> --------------------------------------------------
#>   Group      Obs    Mean     Std. Err.    Std. Dev. 
#> --------------------------------------------------
#>    0        91     52.82       1.1         10.51   
#>    1        109    51.73      0.96         10.06   
#> --------------------------------------------------
#>  combined    200    52.23      0.72         10.25   
#> --------------------------------------------------
#> 
#>            Lower Tail Test           
#>            ---------------           
#>          ratio = sd(0) / (1)         
#>             Ho: ratio = 1            
#>             Ha: ratio < 1             
#> 
#>         Variance Ratio Test          
#> ------------------------------------
#>    F       Num DF    Den DF      p    
#> ------------------------------------
#>  1.0913      90       108      0.6694 
#> ------------------------------------

# using two variables
ifr_ts_var_test(hsb, read, write, alternative = 'less')
#>                Variance Ratio Test                 
#> --------------------------------------------------
#>   Group      Obs    Mean     Std. Err.    Std. Dev. 
#> --------------------------------------------------
#>   read      200    52.23      0.72         10.25   
#>  write      200    52.77      0.67         9.48    
#> --------------------------------------------------
#>  combined    400    52.5       0.49         9.86    
#> --------------------------------------------------
#> 
#>            Lower Tail Test           
#>            ---------------           
#>       ratio = sd(read) / (write)     
#>             Ho: ratio = 1            
#>             Ha: ratio < 1             
#> 
#>         Variance Ratio Test          
#> ------------------------------------
#>    F       Num DF    Den DF      p    
#> ------------------------------------
#>  1.1701     199       199      0.8656 
#> ------------------------------------