& **Yahoo** (search)\
**Google+** &\

Also, each campaign could belong to multiple activity categories, by using multiple tags.

Limitations
-----------

On microworkers.com, there are invite-only campaigns as well. Unfortunately, there is no information freely available on these campaigns or their share of the total number of campaigns. The nature of invite-only campaigns, for which clients apparently hire tested and trusted microworkers, could be a subject for further research.

Some campaigns might have slipped trough between two observations, meaning that their full life cycle very short (only a couple of hours). This does not appear to be typical but cannot be ruled out. Therefore, it can be said that in reality there were possibly more than 7,426 public campaigns and an additional, unknown number of invity-only ones.

As explained above, the campaigns were manually categorized by the author. This categorization, because it relied on objectively observable features of the campaigns, did not require significant subjective judgment. Therefore, in the context of intersubjectivity, it should not be a serious limitation that there was no multiple-person cross-checking performed for interpretation of the category labels.

Finally, there are obviously other brokering platforms for such microtasks, but these are outside the scope of this investigation 