Making Measurement Make Sense (3MS) is a cross-industry initiative founded by the American Association of Advertising Agencies (4A's), the Association of National Advertisers (ANA), and the Interactive Advertising Bureau (IAB). The mission of the Making Measurement Make Sense initiative is to define and drive clear standards-based metrics for interactive advertising, across the marketing ecosystem that are comparable to legacy media.

The Media Rating Council (MRC) is an organization devoted to ensuring that audience measurement is valid, reliable and effective for the media industry and related users. The MRC accomplishes this by setting standards and conducting audits performed by an independent CPA firm to verify compliance with their standards.

The MRC has presented findings that show that in 80% of cases when an impression meets the requirements for viewability, the ad fully renders.

Given the limitations of current technology different ad units, browsers, ad placements, vendors and measurement methodologies yield wildly different viewability numbers.

See more here.

There are many technical challenges that make it impossible to measure all impressions for viewability. Non-measured units that have been shown to have poor measurability include custom skins, native ads, and ads integrated into content, sponsorships, etc., all of which can be highly valued by advertisers. Mobile viewability measurement guidelines have yet to be developed by the industry as well.

The current MRC guidance and the IAB State of Viewability Transaction 2015 position paper apply to browser-based desktop only. The IAB's Mobile Marketing Center of Excellence has asked the MRC about their plan to accelerate the development of standards for mobile measurement. Currently the MRC’s guidance in regards to mobile states: 1) “measurers of viewability of mobile browser-based web ads are encouraged to consider these guidelines in measurements until such time as guidance specifically designed for the measurement of viewability in mobile web based ads is created”, and 2) “... ad impressions served in an in-application environment are currently generally assumed to be viewable.” To note, MRC has already stated publicly that this second assumption is likely inaccurate and that they will be issuing an amendment. Given the measurement challenges that remain untackled in mobile, it is recommended that mobile remain in the “non-measureable” bucket until the MRC provides specific guidance and vendors become accredited against it.:

See more here.

This decision should be made on a case-by-case basis. The IAB State of Viewability Transaction 2015 position paper simply states that "make-good impressions should be both viewable and generally consistent with inventory that was purchased in the original campaign." Ultimately, this is about achieving the goals that you have promised to your client, a key driver of make-good inventory considerations

Large size display ads (such as IAB’s “Rising Stars” formats) present special challenges in terms of meeting the standard viewability thresholds. Because these ads are designed to occupy a large area of the browser page, applying different criteria to determine the viewable status of certain large size ads is reasonable. With this in mind, for display ads sized at 242,500 pixels (which is equivalent to the size of a 970x250 pixel display ad) or greater, a viewable impression may be counted if 30% of the pixels in the ad are on an in-focus browser tab on the viewable space of the browser page for a minimum of one continuous second. If this 30% pixel threshold is used for display ad units of 242,500 pixels or greater instead of the standard 50% pixel threshold, this practice should be fully disclosed to the data users.

The MRC chose not to institute an audibility requirement because the technology doesn’t exist to determine muting in all instances, said David Gunzerath, SVP and associate director of the MRC.

The IAB is encouraging the industry to use a 70% viewability threshold as advocated in the State of Viewability transaction 2015.

See more here.

a. As expressed by the IAB, viewability and fraud are separate issues, both of which are being aggressively addressed by cross-industry efforts by Making Measurement Make Sense (3MS), Trustworthy Accountability Group TAG.
b. From the 3MS: It’s important to note that viewability and fraud are not synonymous. Rather, they are separate issues with small areas of overlap and should be tackled as such. Fraud is about the non-human traffic that skews performance metrics. Viewability is about the opportunity to see.

The IAB State of Viewability Transaction 2015 position paper simply states that "make-good impressions should be both viewable and generally consistent with inventory that was purchased in the original campaign."

See more here.