Measurement
Block rate
Block rate is the share of ad impressions or bid requests prevented from being served or bought because they failed brand-safety, suitability, fraud or targeting checks.
When verification or filtering tools stop an ad from running, or from being bought, that is a block. Block rate is the number blocked divided by the total measured opportunities. It appears in verification reports alongside IVT rate and viewability.
Blocks can happen at different stages: pre-bid (the DSP never bids on flagged requests), or post-bid (the ad was bought, but the verification tag stops the creative rendering in an unsafe or fraudulent environment). Reasons include brand safety categories, brand suitability settings, invalid traffic, geography mismatch or unapproved sites or apps.
A block rate is not automatically good or bad. Very low rates might mean inventory is clean, or that settings are too loose; very high rates can mean settings are too strict, wasting reach and blocking legitimate news, or that the buy is going into poor supply. Post-bid blocks are costlier than pre-bid avoidance because the impression was often already paid for, so buyers aim to move as much filtering as possible to the pre-bid stage.
Think of it like this
Block rate is like the share of items a quality inspector pulls off a production line: too few may mean a sleepy inspector, too many means something upstream is wrong.
An example
A banking brand in Singapore sees a 6% post-bid block rate, mostly for "debated social issues" suitability; after applying the same settings pre-bid, post-bid blocks fall to 1%.
Related terms
Brand safety
Brand safety is the practice of keeping ads away from content that is harmful or universally unacceptable, such as terrorism, child abuse, hate speech or illegal activity, to protect an advertiser's reputation.
Brand suitability
Brand suitability is choosing which content is appropriate for a specific brand's ads, based on its own values and risk tolerance, above the universal floor set by brand safety.
Ad verification
Ad verification is independent third-party measurement that checks whether ads were served to real people, in viewable positions, in safe and suitable environments, and in the intended geographies.
Pre-bid filtering
Pre-bid filtering is checking each ad opportunity for invalid traffic, fraud or brand-safety risk before a buyer bids on it, so bad impressions are avoided rather than refunded later.
IVT rate
IVT rate is the share of measured impressions, clicks or visits identified as invalid traffic, usually shown as a percentage and often split into GIVT and SIVT.
Sources: MRC standards and guidelines