1. Potential biases

2. Poor tracking settings (1/2)
Redirection URLs do not contain media and sources indications.
Traffic is not filtered (your IP address is not excluded from the counting)

3. Poor tracking settings (2/2)
Duration of the session cookie mechanically impacts the number of sessions that are recorded
All pages across the consumer journey should be tracked with the same tool and the same UA. It may include external pages (iFrame).
Single page websites (very common for mini-websites) can not be tracked the ‘standard way’.
Animation tip:
==========
1/ Duration of the session cookie: go to the admin interface to see where this is to be set.
2/ iFrame: show an example of iFrame (opel-promo.fr)

4. IP addresses (1/2)
A user can access the website through his laptop, his mobile and his tablet. Each time he switches from one device to an other, there’s no connection with what he did on the other devices.
In this example, one person is considered as three users.
Please note that this could be partially handled if the user has to authenticate.
Key messages ========= A user can access the website through his laptop, his mobile and his tablet and each time he switches device he is considered a visitor and there’s no connection of what he did in the previous device B2B: same IP address for all employees Key messages ========= For example, your website is accessed by employees working for Coca Cola France and Coca Cola Belgium and they happen to share the same IP Address

5. IP addresses (2/2)
B2B context: employees of a same company / organization often share a common server, thus the same IP address.
As a result, the location provided by GA is not always accurate.
Key messages ========= A user can access the website through his laptop, his mobile and his tablet and each time he switches device he is considered a different user and there’s no connection with what he did in the previous device B2B: same IP address for all employees Key messages ========= For example, your website is accessed by employees working for Coca Cola France and Coca Cola Belgium and they happen to share the same IP Address

6. Other technical issues (1/4)
For some reasons (like browsers not passing on URLs parameters to the webanalytics tool), reports may overestimate the proportion of direct traffic.
Too high proportion of direct traffic:
Mind the consistency of the breakdown by sources.

7. Other technical issues (2/4)
Spammy referral traffic:
Spammy referral traffic: see more details:
Mind the consistency of the breakdown by sources.

8. Other technical issues (3/4)
Spammy referral traffic:
Solution: set a filter to remove this traffic from your reports or use the .htaccess file

9. Other technical issues (4/4)
Tag Manager Implementation
While implementing a tag manager – like Google Tag Manager - , you remove all the tracking codes pasted on the source code of your website to place it on the tag container.
The removal – replacement operation is a bit tricky, and can cause data discrepancy the time everything will be fixed.
A tag is fired when certain conditions are met (that is the trigger).
It can happen that the conditions are not possible anymore (eg : pages on which the tag is supposed to fired have been renamed, …).
In this case, the tag will not fire, and not data will be recorded.