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HUGE discrepancies in numbers when segments are added

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# 1
Visitor ✭ ✭ ✭

Running a report of Sessions / Users / Pageviews for January 1 - August 31, 2016 and comparing with the same time frame for 2015.

 

I'm having an issue, when I turn on my "External Traffic only" filter my All Users pageviews jump from 2.8 million to 3.2 million (external traffic only = 2.2 million). How the number GROWS makes absolutely 0 sense to me - this is all before I turn on the comparison. 

 

THEN when I compare to 2015 my All Users pageviews (for 2016) jump to 3.9 million (external traffic only = 2.2 million).

 

Any insight would be much appreciated.

1 Expert replyverified_user

Re: HUGE discrepancies in numbers when segments are added

Top Contributor
# 2
Top Contributor
Hi,

What you're seeing is caused by data sampling. Sampling kicks in If the number of sessions in the property over the given date range exceeds 500k. Please check the links below for more information about sampling:

https://support.google.com/analytics/answer/2637192?hl=en
https://megalytic.com/blog/understanding-google-analytics-data-sampling
http://www.blastam.com/blog/can-you-trust-your-google-analytics-data

Hope this explains the discrepancies you are experiencing.

Arnold Majlath, Google Analytics Top Contributor
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