Search lost IS (rank) vs Search lost IS (budget)

Google defines both columns as a percentage of time that your ads weren't shown on the Search Network. What differs is the cause Google attributes the time to: poor Ad Rank in the auction for one, insufficient budget for the other. Search impression share, the column beside them, is defined as the impressions you've received on the Search Network divided by the estimated number of impressions you were eligible to receive.

Our reading: one of the three is a ratio of impressions and the other two are percentages of time, so we treat them as three separate measurements of the same campaign rather than three slices of one total. Google does not say they add up to 100, and the units cut against the idea, so the sum is not a check worth running.

The budget column is available at the campaign level only. Google notes that in report editor it is available in the Campaigns report, but not in the Ad group report, and that as of June 2022 it was removed from any previously saved reports that also used 'Ad group', 'Search Keyword', or 'Label (Ad group)'.

The rank column goes missing for a different reason. Google notes that Lost IS (rank) won't be shown on your Ad groups tab if you ran out of budget at any point during the date range being examined.

Our reading: the two traps meet in the same place. On a campaign that hit its budget on even one day of the window, the Ad groups tab shows neither the budget loss nor the rank loss, so a blank there is a missing measurement and not a clean bill of health. Read the pair at campaign level, or pick a window with no budget-out day.

Google's general tips for improving impression share include increasing your campaign budget, increasing your bid, decreasing regional targets and, for Search Network campaigns, improving your ad quality. They are not mapped to a loss column. Google also says impression share is based on an estimate of when your ad was competitive in the auction, and that small fluctuations over time don't necessarily indicate that action is needed.

Our reading: each column names the constraint Google measured. Neither is a prescription, and a loss attributed to rank does not tell you that a budget change would do nothing, so we do not say that here.

This part is Riibon's practice, not Google's. When we roll either column up across days, we do not take a plain average of the daily percentages. Each measured day is weighted by its estimated eligible impressions, which we get by rearranging Google's formula as impressions divided by impression share, worked out inside one Search campaign on an impression count that leaves search partners out, so a quiet day does not count as much as a busy one. Weighting a percentage of time by an impression count is a proxy, and we use it knowingly. A window with no measured day returns no figure rather than an invented mean. The blog post on averaging impression share across days works through the arithmetic.