We get traffic data from Google Analytics based on accesses that media publishers delegate to the PRNEWS.IO widget. The script accesses page statistics daily for 30 days.

PRNEWS.IO uses aggregate statistics describing user activity on the site, such as the number of clicks or page views of a posted publication, namely: ga:sessions, ga:pageviews, ga:timeOnPage.

​Why data cannot be reliably accurate

In some cases, Google uses data sampling technology to reduce the load on its servers. Sampling is a way of forming a representative sample to draw conclusions about the general population. In other words, Google Analytics does not record 100% of the page's sessions, so the data may be biased.
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Moreover, Google Analytics and Facebook take a different approach to attribute clicks and conversions. For example, Google measures visits, and Facebook measures click, which technically is not the same metric. You can read more about this at the link.

There is also the problem of data discrepancy when measuring mobile traffic if it comes from Facebook.