Rupnet Comparisons
I suspect that the Rupnet data is very skewed as follows:
1. It contains no (or very few at least) family-based applications. The USCIS data includes such applications.
2. The participation by Rupnet is incomplete- not everybody updates their stats.
3. People updating Rupnet make mistakes. The data is therefore not 100% correct.
4. The population sample in Rupnet, by definition, excludes those who are not computer-savvy, amoung other factors.
Having said this, the Rupnet data is very useful and I visit the site almost daily. I don't know if the above fully accounts for the differences, though.