Do US visitors have the shortest attention span worldwide?

I’m privileged with having access to the Analytics data of several B2B companies for whom I provide services. This allows me to view, re-view, and analyze the results of online content.

Today, at about the time my head started spinning from all the data, I noticed something. Or at least, I think I did.  While US visitors are always the majority of users (compared to other countries),  they seemed to spend the least time on the site.

This got me curious and I looked at at the web site statistics from ~10 different companies.  These companies have nothing in common in terms of their markets, just that they all appear in my Google Analytics account list. I did not write the content for all of them, so unfortunately, I cannot be blamed for the short attention span. In any case, below are the results from 3 of those companies. (Not enough space for all data.)

While this is by no means a scientific process, it seemed that a similar trend existed in multiple sites — visitors from the US spent on average the least time on site.

Am I missing something? You could initially argue that this was a language problem (it took more time for non native speakers to read). But this argument collapses when comparing visitors from the UK, Australia. or India

I guess this means you need to keep your content short if the majority of your target audience is in North America.

Have you found out the same?