Cronbach's Alpha Reliability Analysis

Computes Cronbach's alpha and prints SPSS-style reliability output including a case processing summary, overall alpha, item statistics, and item-total statistics with alpha-if-item-deleted. Built from scratch with no external package dependencies beyond base R. Handles haven-labelled variables automatically. Detects potentially reverse-coded or misfit items.

Usage

jalpha(
  data,
  ...,
  subset = NULL,
  variable.id = NULL,
  value.id = NULL,
  case.processing.detail = NULL,
  digits = NULL
)

Arguments

data: A data frame.
...: Unquoted variable names (scale items) within data. Use colon notation (e.g. Item1:Item6) to select a range of consecutive columns.
subset: An optional unquoted logical expression (e.g. Group == 1) to subset cases for this call only. Applied after jcomplete and jsubset. Does not affect other function calls.
variable.id: Character or NULL. Variable label display mode: one of "both", "names", "labels", "legend", or "legend.bottom". "names" shows variable names only; "both" shows "name: label"; "labels" shows each item's label in the Item column of the Item Statistics and Item-Total Statistics tables (best for short labels; the returned tables and the reverse-coding diagnostic keep variable names); "legend"/"legend.bottom" keep names and print a label legend after the final table. NULL (default) defers to joutput()'s variable.id setting. Not a logical.
value.id: Not supported by jalpha(). The function does not display value labels, so passing this argument is an error. It exists only to return a clear message rather than misreporting the token as a missing variable. Leave at NULL (default).
case.processing.detail: Per-call override of the Case Processing Summary detail tier: one of "none", "totals", or "per_code". NULL (default) uses the active joutput() level default.
digits: Integer or NULL. Number of decimal places for continuous statistics in the output tables (range 0-7; digits = 0 prints whole numbers with no trailing decimal point). Does not affect p-values, percentages, or integer quantities (counts, N, degrees of freedom), which keep their own fixed conventions. NULL (default) defers to joutput()'s digits setting (default 3).

Value

Invisibly returns a list of class jst_alpha containing: alpha (Cronbach's alpha), n_items, n_used, n_excluded, item_statistics, item_total_statistics, and sample_info (pipeline and missing data counts). item statistics data frame, and item-total statistics data frame.

Details

A red "Reliability Analysis" title is printed first, followed by the case processing summary, overall alpha, item statistics, and item-total statistics.

Examples

# With explicit data frame
jalpha(community, Environment1, Environment2, Environment3,
       Environment4, Environment5)
#> Reliability Analysis
#> 
#> Case Processing    Excluded  Remaining
#>     Original              —        100
#>     Auto-listwise        18         82
#>     Analysis N            —         82
#> 
#> Missing-data breakdown  From 100     %
#>     Environment1
#>       Missing              12     12.0
#>     Environment3
#>       Missing              12     12.0
#> 
#> ──────────────────────────────────────
#> 
#> Reliability Statistics
#> Cronbach's Alpha  N of Items
#> ----------------  ----------
#>            0.297           5
#> 
#> Item Statistics
#> Item           Mean     SD   N
#> ------------  -----  -----  --
#> Environment1  2.988  1.212  82
#> Environment2  2.780  1.228  82
#> Environment3  3.134  1.163  82
#> Environment4  3.098  1.203  82
#> Environment5  2.976  1.474  82
#> 
#> Warning: The following item(s) are negatively correlated with the rest of the scale: Environment2.
#> They may need reverse-coding, or may not belong in the scale - check the item-total table and the item wording.
#> 
#> Item-Total Statistics
#> Item          Corrected Item-Total r  Alpha if Item Deleted
#> ------------  ----------------------  ---------------------
#> Environment1                   0.505                 -0.115
#> Environment2                  -0.615                  0.749
#> Environment3                   0.536                 -0.129
#> Environment4                   0.365                  0.040
#> Environment5                   0.340                  0.012
#> 

# Using juse() default
juse(community)
#> Default data frame set to: community
jalpha(Environment1, Environment2, Environment3, Environment4,
       Environment5)
#> Reliability Analysis
#> Using default data frame: community
#> 
#> Case Processing    Excluded  Remaining
#>     Original              —        100
#>     Auto-listwise        18         82
#>     Analysis N            —         82
#> 
#> Missing-data breakdown  From 100     %
#>     Environment1
#>       Missing              12     12.0
#>     Environment3
#>       Missing              12     12.0
#> 
#> ──────────────────────────────────────
#> 
#> Reliability Statistics
#> Cronbach's Alpha  N of Items
#> ----------------  ----------
#>            0.297           5
#> 
#> Item Statistics
#> Item           Mean     SD   N
#> ------------  -----  -----  --
#> Environment1  2.988  1.212  82
#> Environment2  2.780  1.228  82
#> Environment3  3.134  1.163  82
#> Environment4  3.098  1.203  82
#> Environment5  2.976  1.474  82
#> 
#> Warning: The following item(s) are negatively correlated with the rest of the scale: Environment2.
#> They may need reverse-coding, or may not belong in the scale - check the item-total table and the item wording.
#> 
#> Item-Total Statistics
#> Item          Corrected Item-Total r  Alpha if Item Deleted
#> ------------  ----------------------  ---------------------
#> Environment1                   0.505                 -0.115
#> Environment2                  -0.615                  0.749
#> Environment3                   0.536                 -0.129
#> Environment4                   0.365                  0.040
#> Environment5                   0.340                  0.012
#>

Cronbach's Alpha Reliability Analysis

Usage

Arguments

Value

Details

See also

Examples