Item Discrimination of Moodle Grade Report — item

Calculate Item Discrimination Index of Moodle Grade Report (see Details).

Usage

item_discrim(
  data,
  cor_method = c("pearson", "kendall", "spearman"),
  conf.level = 0.95
)

Arguments

data: (GradesReport) A data frame of class "GradesReport"
cor_method: (Character) A character string indicating which correlation coefficient is to be used for the test. One of "pearson", "kendall", or "spearman", can be abbreviated.
conf.level: (Numeric) Confidence level for the returned confidence interval. Currently only used for the Pearson product moment correlation coefficient if there are at least 4 complete pairs of observations.

Value

A data frame of Item Discrimination Index for each questions.

Details

Item discrimination index (r) is a measure of how well an item is able to distinguish between examinees who are knowledgeable and those who are not. It is a pairwise point-biserial correlation between the score of each questions ("Q" columns) and total score of the quiz ("Grade" column).

item_discrim() calculate the correlation by stats::cor.test() function using Pearson's correlation coefficient (by default), then summarize each parameters into a data frame by broom::tidy(). Different types of correlation can be specified by cor_method argument.

References

What is Item Discrimination Index.

Examples

library(moodleStats)
# Prepare
grades_df_preped <- prep_grades_report(grades_df)

# Calculate
item_discrim(grades_df_preped)
#> # A tibble: 9 × 10
#>   Questions estimate statistic  p.value parameter conf.low conf.high method     
#>   <chr>        <dbl>     <dbl>    <dbl>     <int>    <dbl>     <dbl> <chr>      
#> 1 Q1           0.434      7.89 7.44e-14       269    0.332     0.526 Pearson's …
#> 2 Q2           0.452      8.28 6.15e-15       267    0.351     0.542 Pearson's …
#> 3 Q3           0.600     12.2  1.48e-27       266    0.517     0.671 Pearson's …
#> 4 Q4           0.510      9.68 3.52e-19       267    0.415     0.593 Pearson's …
#> 5 Q5           0.675     14.9  4.13e-37       267    0.604     0.735 Pearson's …
#> 6 Q6           0.646     13.8  3.26e-33       267    0.571     0.711 Pearson's …
#> 7 Q7           0.554     10.9  4.86e-23       267    0.465     0.632 Pearson's …
#> 8 Q8           0.640     13.6  3.59e-32       265    0.563     0.706 Pearson's …
#> 9 Q9           0.597     12.2  1.81e-27       268    0.514     0.669 Pearson's …
#> # … with 2 more variables: alternative <chr>, p.signif <chr>