F-Test for Equality of Variances with Automated Narrative Reporting

Performs an F-test to compare the variances of two independent groups using stats::var.test(), extracts the F-statistic, degrees of freedom, p-value, variance ratio, and confidence interval, and generates a plain-language narrative that includes a practical recommendation for downstream t-test selection (equal vs. unequal variances).

Usage

easy_ftest(
  x,
  y = NULL,
  data = NULL,
  ratio = 1,
  alternative = "two.sided",
  conf_level = 0.95,
  alpha = 0.05
)

Arguments

x: A numeric vector (Group 1), OR a formula outcome ~ group.
y: A numeric vector (Group 2). Ignored when x is a formula.
data: A data frame. Required when x is a formula.
ratio: Hypothesized ratio of variances under H0. Default 1.
alternative: "two.sided" (default), "less", or "greater".
conf_level: Confidence level for the variance ratio CI. Default 0.95.
alpha: Significance threshold for narrative. Default 0.05.

Value

An "easystat_result" object.

Examples

result <- easy_ftest(mpg ~ am, data = mtcars)
#> Multiple parameters; naming those columns num.df and den.df.
print(result)
#> 
#> ================================================================================
#>  EasyStat Result :: FTEST
#> ================================================================================
#> 
#> TABLE 1 — MAIN RESULTS
#> --------------------------------------------------------------------------------
#>                Metric     Value
#>          Variance — 0 14.699298
#>          Variance — 1 38.025769
#>                SD — 0  3.833966
#>                SD — 1  6.166504
#>                 n — 0 19.000000
#>                 n — 1 13.000000
#>    Variance Ratio (F)  0.386561
#>  95% CI lower (ratio)  0.124372
#>  95% CI upper (ratio)  1.070343
#> 
#> TABLE 2 — MODEL FIT / SUMMARY
#> --------------------------------------------------------------------------------
#>          Metric               Value
#>     F-statistic              0.3866
#>    Numerator df                  18
#>  Denominator df                  12
#>         p-value             6.6906%
#>     Alternative           two.sided
#>      Conclusion Variances are EQUAL
#> 
#> ================================================================================
#>  PLAIN-LANGUAGE INTERPRETATION
#> ================================================================================
#> 
#> F-TEST FOR EQUALITY OF VARIANCES Comparison: mpg ~ am
#> 
#> An F-test for equality of variances found not statistically significant (p =
#>   6.6906%) evidence of a difference in variance between the two groups (F(18,
#>   12) = 0.3866). The ratio of variances is 0.3866. The 95% CI for the
#>   variance ratio is [0.1244, 1.0703]. IMPLICATION: The assumption of equal
#>   variances (homoscedasticity) is SUPPORTED. Both the classical t-test and
#>   Welch's t-test are appropriate.
#> 
#> ================================================================================
#>