Alexa and Its Ranking List

I recently read some material talking about the page view ranking of some web sites. It said that the source of the ranking data is alexa.com.

It's good to know source of referenced data but what's the confidence of these data source?

I had a look that website to learn how the ranking list is generated. Here is my understanding:

1. Alexa’s traffic rankings are based on data collected from Alexa Toolbar and other, diverse sources over a rolling 3 month period.

2. A site’s ranking is based on a combined measure of Reach and PageViews.
- Reach is determined by the number of unique Alexa users who visit a site on a given day.
- PageViews are the total number of Alexa user URL requests for a site. However, multiple requests for the same URL on the same day by the same user are counted as a single pageview.

3. Sites with relatively low traffic will not be accurately ranked by Alexa. Traffic rankings of 100,000+ should be regarded as not reliable. Conversely, the closer a site gets to #1, the more reliable its rank. Since Alexa only uses sampled data from all Alexa Toolbar and Alexa Toolbar in fact is just a small portion of the whole Internet user.

So it seems that the ranking list should not be so authoritative as very few people uses its toolbar. But why it gets so popular and important for many VCs? I guess it's mainly due to the lack of other better solutions.

The better data provider should be web browser vendors like Microsoft, Mozilla and Google. But obviously, they are not willing to share with community the data they collected for privacy concerns and potential legal issues.

1. How Reliable Are Your Traffic Ranking?

2. How are Alexa’s traffic rankings determined?

3. About the Alexa Traffic Rankings

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