Let's talk about government data, e.g. data.gov, first. Putting aside "outliers," are most government data sets guided by e.g. "mandates" by the government? If not, how does the fact that say weather, vs. health data are put out by different departments affect difference in quality? Is British or German data quality likely to be either much better or worse than U.S. data?
As between open data from government versus private sources, does the quality of private sector data "converge" to best practices set either by the government or private parties? Or is it "all over the map?"
Data quality can be defined in many ways, but one that I am particularly interested in is metadata standards between various types of databases.