Reach is related to a medium's ratings, generally referred to in the industry as:

The answer to this question is gross ratings points (GRP).
gross ratings points (GRP) is one of the most often used standard  in measuring the impact that we made with our advertising campaign.
To calculate this, we just need to compare the percentage of our target market with the amount of exposure that we get.

The advantage of administering personality tests on employees is that it will allow the employer to know the mindset and personality of the employee. this will allow the employer to at least have an idea as to how the employee works and how his attitude in the workplace. the disadvantage is that it may make the employee a little anxious as to whether he would meet the personality requirements of the employer and whether he would be able to retain the job or not.