Top of page rate is not top impression share

Google's auction insights report has a top of page rate. Google's top and absolute top metrics page defines Search top IS. Both are about the top of the page, and they answer different questions.

Google says top-of-page rate tells you how often your ad, or the ad of another advertiser depending on which row you're viewing, was shown at the top of the page, above the unpaid search results. Its example: 100 impressions, 20 of which appear in any of the positions above the organic search results, is a top-of-page rate of 20%.

Search top impression share is defined differently. Google says it is the impressions that you've received among top ads divided by the estimated number of impressions that you were eligible to receive among top ads. Our reading: the rate asks where the impressions an advertiser got were placed, and the share asks how much of the available top of page opportunity was won.

Google says the auction insights report provides six statistics for Search campaigns: impression share, overlap rate, outranking share, position above rate, top-of-page rate and absolute top of the page rate.

Our reading: because the rate is worked out over an advertiser's own impressions, as Google's 100 impressions example shows, a rival who rarely enters your auctions can post a very high top of page rate from a small number of impressions. Our reading: the same figure on a rival with a large impression share describes far more of the page.

So read the rate with its neighbours on the same row. Our reading: impression share is the column for how much of the opportunity they took. Overlap rate, which Google defines as how often another advertiser's ad received an impression when your ad also received an impression, says how often you actually met.

This is our method, not Google's. Divide a row's absolute top of page rate by its top of page rate.

Google defines the absolute top of page rate as how often an ad was shown at the absolute top of the page as the very first ad above the organic search results. Our arithmetic: the very first ad above the organic results is also above them, so the absolute top rate cannot exceed the top of page rate, and the ratio runs from 0 to 1.

Our reading: a ratio near 1 says the advertiser, when they appear above the organic results, usually appear first. A low ratio says they appear there but rarely lead. Run it on your own row and on a rival's, for the same dates, and the difference is the thing worth discussing, not either rate alone.

Google says search partners don't distinguish between 'top' vs 'others' and aren't included in the auction insights data. It also says the report doesn't show insights when impression share is less than 10%.

Both rates are labelled for Search campaigns only, so they will not appear for Shopping.

Our reading: none of this says why a rival's ads sit where they do. Position above rate, which Google defines as how often the other advertiser's ad was shown in a higher position than yours was, when both of your ads were shown at the same time, is the column that compares the two of you directly.