add K to itemstats

Author: philchalmers

R/itemstats.R

@@ -1,7 +1,8 @@
 #' Generic item summary statistics
 #'
 #' Function to compute generic item summary statistics that do not require
-#' prior fitting of IRT models. Contains information about coefficient alpha
+#' prior fitting of IRT models. Contains information about sample sizes (\code{N}),
+#' number of observed categories (\code{K}), coefficient alpha
 #' (and alpha if an item is deleted), mean/SD and frequency of total scores,
 #' reduced item-total correlations, average/sd of the correlation between items,
 #' response frequencies, and conditional mean/sd information given the
@@ -117,6 +118,7 @@ itemstats <- function(data, group = NULL,
         overall$SEM.alpha <- with(overall, sd_total.score * sqrt(1-alpha))
         rownames(overall) <- ""
         df <- data.frame(N=apply(data, 2, function(x) sum(!is.na(x))),
+                         K=apply(data, 2, \(x) length(unique(na.omit(x)))),
                          mean=colMeans(data, na.rm = TRUE),
                          sd=apply(data, 2, sd, na.rm = TRUE),
                          total.r=itemcor,
@@ -125,6 +127,7 @@ itemstats <- function(data, group = NULL,
     } else {
         overall <- data.frame(N.complete=sum(!is.na(TS_miss)), N=nrow(data))
         df <- data.frame(N=apply(data, 2, function(x) sum(!is.na(x))),
+                         K=apply(data, 2, \(x) length(unique(na.omit(x)))),
                          mean=colMeans(data, na.rm = TRUE),
                          sd=apply(data, 2, sd, na.rm = TRUE))
     }