Why Quantcast Differs From Google Analyticsby Jimmy Boyd
Google Analytics and Quantcast provide free visitor statistics for online properties. Statistics that website owners need to track include the number of unique visitors, number of page views and related data. For various reasons, Quantcast and Google Analytics tend to produce different statistical results. Website owners should be aware of what causes these differences when trying to analyze the accuracy of the competing statistics programs.
Both Google Analytics and Quantcast provide quantified data with the use of a tracking code. You can put this code into your Web page to track direct statistical measurements. When a visitor lands on a page, the code counts that as a visit and collects other information, such as the number of pages viewed in the session. You then access your Quantcast or Analytics account to see the statistics. In this respect, the programs are not substantially different.
Quantcast offers a separate service for those who do not participate in the program to track quantified data. The program for non-quantified data provides public statistics for millions of Web properties. Users of the Quantcast site use the search engine on the main page to look up the name of any website. Each website has its own stats page. A website with a small number of visitors will not necessarily display results due to insufficient data. Google Analytics does not provide non-quantified data. You must use the tracking code to use Analytics, and your statistics are not open to the public.
Sometimes differences arise in the quantified data tracked by each service. Determining which service is more accurate is nearly impossible, but it is clear that Quantcast's model for non-quantified data is less accurate than quantified data. Quantcast advises that its non-quantified data is a "rough" estimate. For proprietary reasons, the company does not release the exact methodology for creating this data. Quantcast recommends using the tracking code for quantified data to get more accurate reporting.
Google provides an opt-out browser add-on for Analytics. Visitors of websites using Quantcast could disable cookies through their personal browsers, but those visitors could also do the same for websites using Analytics. The existence of the Analytics opt-out service provides more opportunity for visitors to disable the cookie. This decreases the veracity of Analytics statistics to some degree.
Other factors may cause differences in quantified data for Quantcast and Google Analytics. First, neither program claims to be perfectly accurate. Statistical tracking is an inexact science, so numbers tend to differ to some degree from program to program. Automated visits from as spider bots, which are programs that visit a website for indexing in search engines and various other online services, also skew the statistics. Depending on how well Analytics and Quantcast differentiate these kinds of visits, you could see differences in visitor data.
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