A recent study by Prof. Joachim Henkel and Dr. Hans Zischka analyzes how many patents are truly valid. The authors ask: If invalidation suits were filed against a random sample of active German patents, what share of these patents would be invalidated? They find that the invalidation rate would be in the same range as for actual invalidation suits that are adjudicated. For 2010 to 2012, these rates are 45% full invalidations, and 33% partial invalidations. The study can be found here, and a summary in German here.
Current Events
"Why most patents are invalid" – Study by Prof. Henkel and Dr. Zischka on patent invalidity