When properly implemented, Quantcast data will line up closely with most web analytics packages—However, there are several common problems that account for the vast majority of issues with data alignment:
• Your tag is not placed on every page of your site. In order for us to accurately measure your site, it is essential that the tag be placed on all pages — consider placing it in a common footer file.
• You are recently Quantified. If we don’t have 30 days worth of data on your website or network, we attempt to project our metrics based on the data that we have seen. For instance, if you Quantified your site on a day with very low traffic, it’s likely that our 30-day projection will appear lower than your actual site traffic. These numbers will converge on your true traffic as we gather more data. An easy way to make sure we are seeing all of your traffic is to log into your Quantcast account, open your profile, and visit the Traffic tab. Click ‘Download traffic stats’ and ensure that the daily page views align fairly closely with your internal analytics.
• Your tag has been removed or malformed since Quantification. Oftentimes our tag is accidentally removed, or altered in a way that interferes with its correct operation, by accident. If you’re experiencing a sudden change in traffic, please ensure that the tag on your site is exactly as it appears in the ‘Network & Setting’ tab of your account, and ensure that it remains on all of the pages of your site.
• You’re using server log data that is counting unique IP addresses. This methodology tends to overstate the number of people visiting a site, as the same Internet user’s IP can change frequently for a large variety of reasons. Quantcast will also not count bots or spiders visiting your website, whereas the IP-based methodology will.
• Terminology varies slightly between different analytics packages. Typically, ‘Pageviews’ is counted fairly evenly across different analytics platforms (although they may appear higher when spider and crawler pageviews are being counted), so that is usually the best metric to use when comparing results. If there is a large difference between the pageviews Quantcast is reporting and the pageviews your analytics package is reporting, it’s most likely indicative of a faulty implementation.