A number of performance factors can be measured in SEM campaigns. These include:
Ad impressions, or how many times the ad is shown
How many times an ad is clicked, or engaged with
How much you pay for every click on an ad
Which keywords drive traffic to your site
How many times your ad is run out of the total number of impressions that are available (impression share)
How many times people saw your ad and clicked through to your site
When you’re interviewing an SEM provider or agency, be sure to ask which metrics they use, which ones they think are the most important, and how those metrics align with and support your business goals.