This function calculates the Cronbach alpha for one or more sets of
psychometric scale items. Each item is a variable in a data frame. Each set
of items is defined by a tidy selection of a set of items.

cronbach(.data, ..., .ci = 0.95)

## Arguments

.data |
A data frame with columns that are psychometric items. |

... |
A set of comma separated tidy selectors that selects sets of
columns from `.data` . For each set of columns, the Cronbach's alpha is
computed. |

.ci |
The value of the confidence interval to calculate. |

## Value

A data frame whose rows are psychometric scales and for each scale,
we have the Cronbach's alpha, and the lower and upper bound of the
confidence interval on alpha.

## Examples

# Return the Cronbach alpha and 95% ci for two scales.
# The first scale, named `x`, is identified by all items beginning with `x_`.
# The second scale, named `y`, is identified by the consecutive items from `y_1` to `y_10`.
cronbach(test_psychometrics,
x = starts_with('x'),
y = y_1:y_10)
#> # A tibble: 2 × 4
#> scale alpha ci_lo ci_hi
#> <chr> <dbl> <dbl> <dbl>
#> 1 x 0.620 0.452 0.788
#> 2 y 0.738 0.626 0.850