alexa

As a webmaster or a marketer, you may wonder why the reports of web traffics you get from Google Analytics can differ from results you obtain with Alexa.com.

Let me give you some explanations about the differences between these two tools.

How does Alexa estimate website traffic ?

Alexa actually uses a toolbar to measure website statistics. Once someone installed it, the toolbar collects data on browsing behavior which is transmitted to Alexa's website where it is stored and analyzed.

This information is the basis for the company's web traffic reporting but other data sources beyond Alexa Toolbar are taken into account (I guess those could be domain name age, number of indexed pages in search engines, etc.).

How does Google Analytics work ?

Google Analytics works with a 'page tag', a hidden snippet of JavaScript code (Google Analytics Tracking Code) that the user adds onto every page of his or her website. This code acts as a beacon, collecting private visitor data and sending it back to Google data collection servers for processing in almost real-time.

In addition, the GATC sets first party cookies on each visitor's computer. This is used to store information such as whether the visitor has been to the site before (new or returning visitor) and what was the referrer site or campaign the visitor came from e.g. search engine, email etc.

Why Google Analytics and Alexa are different

As you could read above, Google Analytics and Alexa use quite different systems to estimate website traffic, therefore it's not surprising if they obtain different results.

First, regarding Alexa, it's clear that the system has its limits: Alexa largely depends on the number of people using its toolbar. There can be some controversy over how representative Alexa's user base is of typical Internet behavior, notably for low-traffic sites. The largest is the community, the more accurate the data are. Unfortunately, Alexa doesn't provide information on the number of Alexa Toolbar active users (it could be something like several millions).

Second, concerning Google Analytics, the largest potential impact on data accuracy comes from users deleting or blocking cookies. Without cookies being set, Google Analytics cannot collect data. Plus, many ad filtering programs and extensions (such as Firefox's Adblock) can block the GATC. This prevents some users from being tracked, and leads to holes in the collected data.

Another limitation of Google Analytics for large websites is the use of sampling in the generation of many of its reports. To reduce the load on their servers and to provide users with a relatively quick response for their query, Google Analytics indeed limits reports to 200,000 randomly sampled visits at the profile level for its calculations.

As a conclusion, Google Analytics appears more accurate for small and medium-traffic websites than Alexa, but the latter can provide good estimations for websites having more traffic.