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Minor bug: Default method in item_intercor() is 'pearson', not 'spear…
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…man' (#610)
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strengejacke authored Sep 10, 2023
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29 changes: 14 additions & 15 deletions R/item_intercor.R
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#' @param x A matrix as returned by the `cor()`-function,
#' or a data frame with items (e.g. from a test or questionnaire).
#' @param method Correlation computation method. May be one of
#' `"spearman"` (default), `"pearson"` or `"kendall"`.
#' `"pearson"` (default), `"spearman"` or `"kendall"`.
#' You may use initial letter only.
#'
#' @return The mean inter-item-correlation value for `x`.
#'
#' @details This function calculates a mean inter-item-correlation, i.e.
#' a correlation matrix of `x` will be computed (unless
#' `x` is already a matrix as returned by the `cor()`-function)
#' and the mean of the sum of all item's correlation values is returned.
#' Requires either a data frame or a computed `cor()`-object.
#' \cr \cr
#' \dQuote{Ideally, the average inter-item correlation for a set of
#' items should be between .20 and .40, suggesting that while the
#' items are reasonably homogeneous, they do contain sufficiently
#' unique variance so as to not be isomorphic with each other.
#' When values are lower than .20, then the items may not be
#' representative of the same content domain. If values are higher than
#' .40, the items may be only capturing a small bandwidth of the construct.}
#' \cite{(Piedmont 2014)}
#' @details This function calculates a mean inter-item-correlation, i.e. a
#' correlation matrix of `x` will be computed (unless `x` is already a matrix
#' as returned by the `cor()` function) and the mean of the sum of all items'
#' correlation values is returned. Requires either a data frame or a computed
#' `cor()` object.
#'
#' "Ideally, the average inter-item correlation for a set of items should be
#' between 0.20 and 0.40, suggesting that while the items are reasonably
#' homogeneous, they do contain sufficiently unique variance so as to not be
#' isomorphic with each other. When values are lower than 0.20, then the items
#' may not be representative of the same content domain. If values are higher
#' than 0.40, the items may be only capturing a small bandwidth of the
#' construct." _(Piedmont 2014)_
#'
#' @references
#' Piedmont RL. 2014. Inter-item Correlations. In: Michalos AC (eds)
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29 changes: 14 additions & 15 deletions man/item_intercor.Rd

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