Having an extra pair of eyes monitoring play in each area had a preventive effect and promoted better decision making on suspected fouls.

BBC: Uefa trials new refereeing system

In theory, this gives the advertiser a better feel for the effect that ad had on those other 999 viewers who did not click on it.

FORBES: Magazine Article

The Better Living Information Centre found that a third of the products that it tested had no discernible effect on them.

ECONOMIST: The Japanese are a super-clean lot. Obsessively so?