Skip to contents

Assumption checks for one-sample t-test

check_assumptions.Rd

Check normality and outliers for a numeric sample, as typically required for a one-sample t-test on a population mean with unknown variance.

Usage

check_assumptions(x, alpha = 0.05, verbose = TRUE)

Arguments

x

A numeric vector of observations.

alpha

Significance level for the Shapiro–Wilk normality test.

verbose

Logical; if TRUE, prints a short textual summary of the results to the console.

Value

A list of class "oneMeanTest_assumptions" with components:

shapiro

List with W statistic, p-value, alpha, and a logical flag normal indicating if normality is acceptable (or NA if the test was not run).

outliers

Numeric vector of detected outliers (possibly empty).

n

Sample size after removing NA values.

normal

Logical flag indicating if normality is acceptable (TRUE / FALSE), or FALSE if the Shapiro–Wilk test rejects at the chosen alpha.

message

Textual summary of the diagnostics.

Details

The function performs a Shapiro–Wilk normality test (when the sample size is between 3 and 5000) and detects outliers using the 1.5*IQR rule. It is used inside one_mean_test when check_assumptions = TRUE.

Examples

set.seed(123)
x <- rnorm(30, mean = 5, sd = 2)

# Verbose output
check_assumptions(x, alpha = 0.05, verbose = TRUE)
#> Normality appears acceptable based on the Shapiro-Wilk test. No outliers detected by the 1.5*IQR rule. 
#> $shapiro
#> $shapiro$W
#> [1] 0.9789351
#> 
#> $shapiro$p.value
#> [1] 0.7965839
#> 
#> $shapiro$alpha
#> [1] 0.05
#> 
#> $shapiro$normal
#> [1] TRUE
#> 
#> 
#> $outliers
#> numeric(0)
#> 
#> $n
#> [1] 30
#> 
#> $normal
#> [1] TRUE
#> 
#> $message
#> [1] "Normality appears acceptable based on the Shapiro-Wilk test. No outliers detected by the 1.5*IQR rule."
#> 
#> attr(,"class")
#> [1] "oneMeanTest_assumptions"

# Silent output (used internally by one_mean_test)
a_res <- check_assumptions(x, alpha = 0.05, verbose = FALSE)
a_res
#> $shapiro
#> $shapiro$W
#> [1] 0.9789351
#> 
#> $shapiro$p.value
#> [1] 0.7965839
#> 
#> $shapiro$alpha
#> [1] 0.05
#> 
#> $shapiro$normal
#> [1] TRUE
#> 
#> 
#> $outliers
#> numeric(0)
#> 
#> $n
#> [1] 30
#> 
#> $normal
#> [1] TRUE
#> 
#> $message
#> [1] "Normality appears acceptable based on the Shapiro-Wilk test. No outliers detected by the 1.5*IQR rule."
#> 
#> attr(,"class")
#> [1] "oneMeanTest_assumptions"