individual_differences function

Test individual differences

individual_differences(dataSrc, predicate = NULL)

Arguments

• dataSrc: a connection to a dexter database, a matrix, or a data.frame with columns: person_id, item_id, item_score
• predicate: An optional expression to subset data, if NULL all data are used.

Returns

An object of type tind. Printing the object will show test results. Plotting it will produce a plot of expected and observed score frequencies. The former under the hypothesis that there are no individual differences.

Details

This function uses a score distribution to test whether there are individual differences in ability. First, it estimates ability based on the score distribution. Then, the observed distribution is compared to the one expected from the single estimated ability. The data are typically from one booklet but can also consist of the intersection (i.e., the common items) of two or more booklets. If the intersection is empty (i.e., no common items for all persons), the function will exit with an error message.

Examples

db = start_new_project(verbAggrRules, ":memory:")
add_booklet(db, verbAggrData, "agg")

dd = individual_differences(db)
print(dd)
plot(dd)

close_project(db)