Which media metric measures how many unique people were exposed to an advertisement at least once?

• A. Click-through rate
• B. Impressions
• C. Frequency
• D. Reach

Answer: (D)

The key idea is audience exposure—how many unique individuals actually saw the advertisement. Reach counts distinct people who were exposed at least once, which is exactly what this question is asking for. Impressions, on the other hand, tally every display of the ad, including multiple views by the same person, so they can overstate how broad the audience is. Frequency takes those impressions and divides by reach to show the average number of times each exposed person saw the ad. Click-through rate measures engagement by looking at the share of people who clicked after seeing the ad, not how many unique people saw it. So reach is the metric that answers how many unique people were exposed at least once.