Exam IIA-CIA-Part3 topic 2 question 389 discussion

An internal auditor was assigned to test for ghost employees using data analytics. The auditor extracted employee data from human resources and payroll. Using spreadsheet functions, the auditor matched data sets by name and assumed that employees who were not present in each data set should be investigated further. However, the results seemed erroneous, as very few employees matched across all data sets. Which of the following data analytics steps has the auditor most likely omitted?