How much is viewability impacting your online advertising? According to a new whitepaper from comScore called “The Value of a Digital Ad,” it could be quite a lot.

ComScore says that, unlike with other channels, gross reach and frequency numbers are often inadequate and misleading because they take non-viewable and fraudulent traffic into account. According to fourth quarter 2015 numbers from comScore’s vCE insights in the U.S., 48% of digital display and video campaign ads were viewable, 45% were not viewable by humans and 7% were non-viewable and had invalid traffic when measured with gross attitudinal numbers.

The company says that validated reach and frequency reports may lead to lower numbers, but are more accurate and mean less wasted dollars. Validating ad impressions removes the non-viewable and invalid impressions.

According to the company’s whitepaper, which analyzed 109 large branding campaigns, validated reach cut numbers by 35% for the population overall and 23% for the primary target audience.

The whitepaper compared brand lift seen by digital campaigns using gross attitudinal numbers with those using validated ones and found a linear relationship between effectiveness and viewability.

Generally, brand lift maxes out on digital advertising around 15 to 20 impressions. That’s compared with TV ads, which the whitepaper says maxes out at about three to five exposures.

Based on gross attitudinal numbers, at six exposures to a digital ad, the brand could see a 3.0 point lift, at 10 exposures a 5.7 point lift and a 7.5 point lift at 16 exposures.

Those numbers actually improve when campaigns use validated numbers instead of gross attitudinal ones. When using validated numbers, brands experiences a 6.0 point lift at six exposures, which is higher than the brand lift number for 10 exposures when using gross attitudinal numbers.

Effectiveness curves vary by campaign, but generally digital ads continue to see meaningful lifts through at least 10 viewable exposures. Declining effectiveness for digital campaigns happens around 50 validated exposures overall. To avoid wearing consumers out with their ads comScore recommends marketers implement frequency caps at a max of 50 exposures.