There are advantages and disadvantages to all methods of web data collection, be that javascript page tagging or log file analysis (or packet sniffing – but I will leave packet sniffing for my next post).

Have I missed any out? Which do you prefer? My preference is for a hybrid model with a web analytics solution that uses both javascript page tagging and log files (remember there can be political reasons too – for some big companies they like keeping control of their web data so a pure page tagging model is not ideal).

Page Tagging Advantages                                                     

Measure events in Web 2.0 rich Internet applications built with Ajax or Flash

Measure traffic on portions of your site embedded in other web sites where you don’t have access to logs

Track page views even if they were cached in ISP proxy servers

Track page views following a click on the browser’s back button 

Measure behavior within web pages, such as scrolling down or changing form fields

Measure shopping cart activity

Measure client side information, such as the browser’s screen size, etc.

Capture additional information items such as user login names or form field data that are passed through customized tags 

Breaks through proxy and caching servers – provides more accurate session tracking

Client side capture of ecommerce data – server side access can be problematic

Visitor data can be collected in near real time

Page Tagging Disadvantages

Set up errors lead to data loss and you can’t go back in time, if you make a mistake with your tagging you have a hole in your data

Firewalls can mangle or restrict tags

Cannot track bandwidth or completed downloads, tags are set when the page/file/event is requested not when the download is completed (although you can tag different stages of an event/file)

Log Files Advantages

Historical data can be processed easily

No firewall issues to worry about

Can track bandwidth and completed downloads and differentiate between completed and partial downloads

Monitor paths and drop-off points of search engine robots that index your site to help you with search engine optimization

Capture click fraud activity that does not execute JavaScript and remains invisible to page tags

Monitor page delivery performance, abandoned page views, and incomplete downloads

Securely capture http user names

Load historical information from before page tagging

Avoid the effort of modifying your web pages and scripted pages for inserting tags and then acceptance testing the modifications

Avoid the effort of monitoring your site for pages that are missing page tags

Measure views, for example, of your PDF documents that were directly found and clicked from search engines such as Google

Measure mobile browsers/visitors which may not fire JavaScript page tags

Measure page views even if the viewer clicked on to the next page before the page tag fired

Log file disadvantages

Proxy/caching inaccuracies, if a page is cached, no record is logged on your web server

No event tracking, no javascript, flash or AJAX tracking

Time consuming web server log file management and log file transfer from disparate web server farms

Thanks so much for reading and let me know if you think there are advantages or disadvantages to either that I haven’t mentioned.