Main Table
The table below summarises summary statistics regarding the clarity of each item. It contains mean clarity (scale from 1 - Very unclear to 7 - very clear), SD, median, MAD, but also Floor: the % of people who picked 1, and Ceiling: the % of people who picked 7. It also describes from how median does the mean clarity of the items deviate from an ideal clarity score of 6.5/7 (i.e., between Quite clear and very clear) -> See column z_ideal.
# 4. Compute per-item diagnostics
item_stats <- df_long %>%
group_by(Item) %>%
summarise(
Mean = mean(value, na.rm = TRUE),
SD = sd(value, na.rm = TRUE),
Median = median(value, na.rm = TRUE),
MAD = mad(value, na.rm = TRUE),
Floor = 100 * mean(value == 1, na.rm=TRUE), # % of people who picked 1
Ceiling = 100 * mean(value == 7, na.rm=TRUE), # % of people who picked 7
.groups = "drop"
) %>%
mutate(
z_median = (Mean - median(Mean)) / mad(Mean),# how many MADs above (if positive) or below (if negative) an item’s mean sits relative to the central mass of item-means
z_Ideal = (Mean - 6.5) / mad(Mean),# how many MADs above (if positive) or below (if negative) an item’s mean sits relative to the ideal Scale point of 6.5
IQR_flag = Mean < (quantile(Mean, .25) - 1*IQR(Mean)) | # We use 1*IQR --> This is more conservative than your usual 1.25*IQR
Mean > (quantile(Mean, .75) + 1*IQR(Mean))
)
# show all rows, with search/filter, horizontal scrolling
datatable(
item_stats,
options = list(
pageLength = nrow(item_stats), # default to show all rows
scrollX = TRUE, # allow horizontal scrolling
autoWidth = TRUE # auto‐adjust column widths
),
class = "stripe hover compact",
rownames = FALSE
)
From this table, we can see several important things: - Most items have a satisfying mean (M > 6) and/or satisfying median (median = 6.5 or 7, i.e., at least 50% of the sample gave the item the maximum score of 7) - 6 items are flagged as outliers using 1*IQR distance or 2 MAD below the median of the sample (see z-scores). - With the exception of 1 outlier, these items are in the General Villain evaluation.
I FLAGGED AS PROBLEMATIC (i.e., to delete or to revise) items deviating from more than 2 MAD from an ideal mean comprehension score of 6.5.