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,
  print = 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. Written in R syntax and checked the way jsubset() checks a filter: subset = NOT(Age < 40), for example, is refused with the corrected subset = !(Age < 40) shown (see jsubset for a translation table).
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 report value.id as a variable that was not found. 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. The Case Processing table itself prints only when a filter or listwise deletion excluded cases; otherwise a one-line N statement takes its place. See ?joutput (case.processing).
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).
print: Logical or NULL. FALSE prints nothing – no table, no title, no note – and returns the result as every call does; errors and warnings still show. TRUE prints even under joutput("silent"). NULL (the default) prints unless the level is silent. For a script that keeps many results and wants no output: see joutput.

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             --        103
#>     Auto-listwise        19         84
#>     Analysis N           --         84
#> 
#> Missing data   From 103    %
#>     Environment1
#>       Missing     12     11.7
#>     Environment3
#>       Missing     12     11.7
#> --------------------------------------
#> 
#> Reliability Statistics
#> Cronbach's Alpha  N of Items
#> ----------------  ----------
#>       0.348            5
#> 
#> Item Statistics
#> Item           Mean    SD    N
#> ------------  -----  -----  --
#> Environment1  3.131  1.180  84
#> Environment2  2.869  1.180  84
#> Environment3  3.060  1.226  84
#> Environment4  3.333  1.186  84
#> Environment5  2.762  1.470  84
#> 
#> Warning: The following item is negatively correlated with the rest of the
#> scale: Environment2.
#> It 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           0.510                  -0.006
#> Environment2          -0.660                   0.783
#> Environment3           0.539                  -0.052
#> Environment4           0.447                   0.056
#> Environment5           0.455                  -0.030
#> 

# The data frame may also be given by name
jalpha(data = community, Environment1, Environment2, Environment3,
       Environment4, Environment5)
#> Reliability Analysis
#> 
#> Case Processing    Excluded  Remaining
#>     Original             --        103
#>     Auto-listwise        19         84
#>     Analysis N           --         84
#> 
#> Missing data   From 103    %
#>     Environment1
#>       Missing     12     11.7
#>     Environment3
#>       Missing     12     11.7
#> --------------------------------------
#> 
#> Reliability Statistics
#> Cronbach's Alpha  N of Items
#> ----------------  ----------
#>       0.348            5
#> 
#> Item Statistics
#> Item           Mean    SD    N
#> ------------  -----  -----  --
#> Environment1  3.131  1.180  84
#> Environment2  2.869  1.180  84
#> Environment3  3.060  1.226  84
#> Environment4  3.333  1.186  84
#> Environment5  2.762  1.470  84
#> 
#> Warning: The following item is negatively correlated with the rest of the
#> scale: Environment2.
#> It 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           0.510                  -0.006
#> Environment2          -0.660                   0.783
#> Environment3           0.539                  -0.052
#> Environment4           0.447                   0.056
#> Environment5           0.455                  -0.030
#> 

# 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             --        103
#>     Auto-listwise        19         84
#>     Analysis N           --         84
#> 
#> Missing data   From 103    %
#>     Environment1
#>       Missing     12     11.7
#>     Environment3
#>       Missing     12     11.7
#> --------------------------------------
#> 
#> Reliability Statistics
#> Cronbach's Alpha  N of Items
#> ----------------  ----------
#>       0.348            5
#> 
#> Item Statistics
#> Item           Mean    SD    N
#> ------------  -----  -----  --
#> Environment1  3.131  1.180  84
#> Environment2  2.869  1.180  84
#> Environment3  3.060  1.226  84
#> Environment4  3.333  1.186  84
#> Environment5  2.762  1.470  84
#> 
#> Warning: The following item is negatively correlated with the rest of the
#> scale: Environment2.
#> It 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           0.510                  -0.006
#> Environment2          -0.660                   0.783
#> Environment3           0.539                  -0.052
#> Environment4           0.447                   0.056
#> Environment5           0.455                  -0.030
#>

Cronbach's Alpha Reliability Analysis

Usage

Arguments

Value

Details

See also

Examples