Nielsen:

Nielsen is well-established in the industry, having been a dominant player in TV audience measurement for decades. It is often considered the industry standard, particularly for traditional linear TV.

Methodology

• Nielsen primarily uses a panel-based approach, where a sample of households is selected to represent the broader population. Depending on market size, the methodology can have more enhancements:  local people meters that require viewers to indicate who is watching, set meters that are directly installed in homes that are part of a representative sample, code readers that can detect audio, and return path data that collects data from partnerships with cable and satellite providers via boxes in homes. 

Strengths

• Offers detailed demographic information, which is important when targeting specific age and gender segments. The long-standing methodology provides consistency and comparability to track trends.

Limitations

• Relies on a relatively small sample size, which may not fully capture niche audiences. In large to mid-sized markets, data can be available within days, while in mid-smaller markets, data processing and delivery is typically about a month after conclusion of each 4-week measurement period.

Comscore:

Comscore is the newer player in TV measurement compared to Nielsen, but has a strong background in digital measurement. Known for providing alternative metrics, such as behavioral.

Methodology

• Comscore offers a much larger sample size, using a census-based approach collecting data from set-top boxes and smart TVs. Data is collected passively from devices, which reduces the reliance on viewers self-reporting and minimizes sample bias. 

Strengths

• The larger sample provides data from far more homes, capturing a broader and more diverse cross-section of the viewing population. In the medium-small size DMAs, viewing insights are available sooner than they are with Nielsen data.

Limitations

• While growing, Comscore’s TV ratings are not as universally accepted as Nielsen’s, which can make it harder to use as a sole currency for buying ads. It is focused more on household data: “presence of” a certain behavior or age range within the household, attributing viewing to the household rather than target demographic.

Knowing the differences is important, especially when transacting with a combination of the two.  Is there a formula that can be used to make the data more apples to apples?  In short, no.  While the same thing is being measured – the methodology is completely different.  Think of it this way:  you hire two photographers to capture the same subject.  One photo is black and white, taken up close to capture specific details.  The other is in color, a wide shot, that gives a more broad perspective.  Both captured what they were supposed to, but in a very different way.

Which is better?  Ultimately it depends on your goals and what is important to you.