I had a great chat (as always) with Eric Enge about a set of web analytics research numbers of his; where part of the dialogue kept coming back to elements of JavaScript being Enabled or Disabled. During the chat I promised that we would do a cross analysis among a larger set of visits (not visitors), for us to get a decent attitude on what the JavaScript Disabled index number should be.

The whole reason that this might be of interest is; that most users of Web Analytics enterprise systems today deploy a page tagging solution such as Omniture or IndexTools – where the data collection methodology is in part based on a small JavaScript. It is therefore very likely that there will be a discrepancy in the collected data if you have visitors who have disabled JavaScript. Before concluding on the impact of this understood discrepancy, let me present the results:

JavaScript Disabled Index numbers
EU: 1.4%
US: 3.05%

Source: 1.000.000.000 visits across multiple industry web properties using IndexTools.
(VisualRevenue.com/blog – Dennis R. Mortensen)

Where one might, at first sight, be concerned about a 2% to 3% discrepancy, due to the fact that JavaScript is not enabled. This is normal and it is very common that people confuses or transmit to much value to JavaScript disabled numbers as they either expect NO data collection at all or very limited data collection. The fact is that most (all the ones I know) of the enterprise vendors have a noscript IMAGE “fall-back” data collection methodology – meaning that all of those who have JavaScript disabled will be tracked!

It is however valid to say that the IMAGE fall-back methodology do not have the same degree of nuance (the number of metrics) as the original intended JavaScript. But all the basic information is collected and tied together in a session. You might (dependant on your Web Analytics solution) even be able to configure the fall-back methodology to track custom actions, revenue and other information.

Therefore and as example, if we say you have a cool 4% sales conversion rate on your US visitors, the discrepancy in your Revenue Metric (KPI) should not be off more than 3.05% of your 4% and thus you cannot attribute JavaScript Disabled discrepancy to more than 0.12% of your Revenue Metric. On $1,000,000 in sales, that is only $1,220 - AND some vendors even give you an opportunity to track those last $1,220 as well :-)

Conclusion:
It is very likely for us to believe that we will see a continuous decline in visitors who have JavaScript Disabled and it is very fair to trust that visitors with JavaScript Disabled have little or no impact on your web analysis efforts. However; it is a fact that data might not be 100% accurate due to this data collection defect, but the impact is much smaller than the immediate believed 2% to 3% as first assumed.

So what are your JavaScript Disabled numbers; are they close to my index numbers or… am I completely off? :-)
Comments please. (especially if you have some RAW numbers on IMAGE disabled)

N.B.
I checked my blog and by pure luck, the JavaScript Disabled number for US visitors matched the Index Number almost spot on.