A nurse on a quality control committee is evaluating the results of recently implemented measures designed to reduce client medication errors. Which of the following methods should the nurse use to evaluate the success of the changes?

Conduct a study about the time and money costs of implementing the change.

Provide the staff with a questionnaire to quantity staff satisfaction with the changes.

Compare the number of medication errors before and after the action was implemented.

Establish a benchmark to identify a standard of performance.