Attribution
Click-through rate
Also called CTR.
Click-through rate is clicks divided by impressions for an ad, a result, or a link. It tells you how often a shown thing was clicked.
How it is measured
Count impressions and clicks from the same system and the same window, then divide. The rate for search listings comes from the search console; for ads it comes from the ad platform; for email it uses delivered or opened as the base.
State the base. Email CTR on delivered differs from CTR on opened. A listing's CTR depends heavily on its position, so compare like positions.
Worked example
A bike-repair shop's page for 'flat tire repair' is shown 18,600 times in search over a month and clicked 744 times: 4.0 percent. Its average position is 3.2.
A rewrite of the title tag to include the neighborhood and the price lifts clicks to 1,023 on 19,100 impressions, 5.4 percent, with position unchanged. The shop's phone bookings from that page rise by about a third.
How it differs
Click-through rate needs an impression as the denominator. Without a count of exposures, clicks cannot be rated. An impression is a chance to click; the rate is what people did with it.
Common errors
Comparing CTR across positions. Mixing email bases. Chasing CTR while ignoring conversion. Counting accidental or bot clicks. Reading a rate off a few dozen impressions.
In practice
Review CTR by query or ad against position. Rewrite the listings with low CTR for their rank. Check that the click leads somewhere that fulfills the promise.