Mood's Median Test: Grouped (x_by)

The x_by implementation tests whether a continuous variable's population median differs across the levels of a grouping variable.

Arguments

mmdtest_def_xby's baseline fn takes .proc plus an optional custom_median forwarded through ... in MEDIAN_TEST().

Variants

"multi"

Runs one Mood's median test per grouping variable when group from x_by() selects multiple variables. Accepts custom_median (applied identically to every grouping variable's test) and display_var, a 1-based index (default 1L, the first grouping variable) choosing which grouping variable's contingency table is computed and shown; pass display_var = FALSE to skip it entirely. Only the selected variable's table is retained on the returned object, so re-run with a different display_var to inspect another one.

Grouped Mood's Median Test default class

Both base and multi return a class_median_test object. base always has one grouping variable, so cont_tab holds its one table. multi has as many statistic/df/p_value entries as grouping variables, but cont_tab holds only the one display_var selected (or none, if display_var = FALSE).

See also

Other mmdtest-implementations: mmdtest-on

Examples

box::use(
    statim[define_model, prepare, via, conclude]
)

set.seed(123)
x = rcauchy(50, 1, 1.5)
g1 = sample(letters[1:5], size = 50, replace = TRUE)
g2 = sample(c("control", "treatment"), size = 50, replace = TRUE)

MEDIAN_TEST(x_by(x, g1))
#> -- Summary ---------------------------------------------------------------------
#> 
#> ────────────────────────────────
#>   vars  statistic  df  p_value  
#> ────────────────────────────────
#>    g1     3.066    4    0.547   
#> ────────────────────────────────
#> 
#> 
#> -- Contingency Table -----------------------------------------------------------
#> 
#>                            Cross Tabulation: x by y              
#>               ───────────────────────────────────────────────────
#>                                            y              
#>               ───────────────────────────────────────────────────
#>                 x                  d   e    c   a    b    TOTAL  
#>               ───────────────────────────────────────────────────
#>                 > Median (1.04)    4   5    3   5    8     25    
#>               
#>                 <= Median (1.04)   5   6    5   6    3     25    
#>               ───────────────────────────────────────────────────
#>                 TOTAL              9   11   8   11   11    50    
#>               ───────────────────────────────────────────────────
#> 

# show g1's contingency table
define_model(x_by(x, g1)) |>
    prepare(MEDIAN_TEST) |>
    conclude()
#> 
#> == Model ======================================================================= 
#> 
#> Variable Mapper : x_by 
#> Args : x | g1 
#>     x_vars : 1 
#>     by_vars : 1 
#> 
#> == Mood's Median Test ========================================================== 
#> 
#> -- Summary ---------------------------------------------------------------------
#> 
#> ────────────────────────────────
#>   vars  statistic  df  p_value  
#> ────────────────────────────────
#>    g1     3.066    4    0.547   
#> ────────────────────────────────
#> 
#> 
#> -- Contingency Table -----------------------------------------------------------
#> 
#>                            Cross Tabulation: x by y              
#>               ───────────────────────────────────────────────────
#>                                            y              
#>               ───────────────────────────────────────────────────
#>                 x                  d   e    c   a    b    TOTAL  
#>               ───────────────────────────────────────────────────
#>                 > Median (1.04)    4   5    3   5    8     25    
#>               
#>                 <= Median (1.04)   5   6    5   6    3     25    
#>               ───────────────────────────────────────────────────
#>                 TOTAL              9   11   8   11   11    50    
#>               ───────────────────────────────────────────────────
#> 

# more than one grouping variable requires "multi"; shows g2's table
define_model(x_by(x, c(g1, g2))) |>
    prepare(MEDIAN_TEST) |>
    via("multi", display_var = 2L) |>
    conclude()
#> 
#> == Model ======================================================================= 
#> 
#> Variable Mapper : x_by 
#> Args : x | g1, g2 
#>     x_vars : 1 
#>     by_vars : 2 
#> 
#> == Mood's Median Test · multi ================================================== 
#> 
#> -- Summary ---------------------------------------------------------------------
#> 
#> ────────────────────────────────
#>   vars  statistic  df  p_value  
#> ────────────────────────────────
#>    g1     3.066    4    0.547   
#>    g2     5.128    1    0.024   
#> ────────────────────────────────
#> 
#> 
#> -- Contingency Table -----------------------------------------------------------
#> 
#>                            Cross Tabulation: x by y          
#>                   ───────────────────────────────────────────
#>                                         y             
#>                   ───────────────────────────────────────────
#>                     x           treatment   control   TOTAL  
#>                   ───────────────────────────────────────────
#>                     > Median        9         16       25    
#>                   
#>                     <= Median      17          8       25    
#>                   ───────────────────────────────────────────
#>                     TOTAL          26         24       50    
#>                   ───────────────────────────────────────────
#>