During the early years (2001-2003), when most of laboratory facilities had not been launched and crews were limited to three, there was less research activity. Activity also decreased during the post-Columbia period of two-person caretaker crews (2003-2007). However, as station assembly resumed and crews expanded to six, both new and ongoing projects increased significantly, and are expected to increase in the next few years.
Moreover, ISS projects are generally managed by academic or corporate researchers, with a low level of all-NASA or joint projects.

(Graph by William Bianco.)
These percentages have been relatively stable since the beginning of crewed operations. Most ISS research should be described as a collaboration between the government and private sector, where the government provides a unique, expensive experimental apparatus to which outside scientists and engineers bring research questions that can only be answered in an orbital environment.
Finally, here is the publication output of ISS research:

(Graph by William Bianco.)
The first bar shows the current (October 2013) rate of publication success – somewhat less than 50 percent. However, most of the projects in the database are either ongoing or will commence operations at a future date, and thus cannot be expected to have produced publishable findings as of yet. To correct for this bias, the second bar gives the predicted publication rate for ISS projects based on a statistical analysis that accounts for the identity of project PIs, the start date, and whether research was conducted during assembly of the ISS. With these factors taken into account, the predicted publication rate is well over 90 percent, which is notable given that many journals have acceptance rates below 10 percent.
There is no guarantee that research on the ISS will cure cancer, end global warming, or earn their PIs a Nobel Prize. However, the data show that ISS research satisfies the basic conditions for good science: attracting outside researchers, engaging disciplinary debates, and generating publishable results. It is unrealistic to judge the ISS based on its short-term payoff; by that standard, virtually all basic research in the sciences would be judged a failure. Even given the data presented here, reasonable people can disagree about the benefits and costs of continued ISS operations. But to make a judgment about the long-term value of the ISS barely three years after its completion makes no more sense than tearing up a lottery ticket a week before the drawing.