A few of these papers also looked at the impact of receiving VC financing on subsequent patenting (shown in Appendix Table A-2). The majority find only a weak or even negative association with VC involvement or the level of financing, controlling for prior patenting. Engel and Keilbach (2004) compare German VCbacked firms with a control group of non-VC-backed firms matched on industry ,founding year, size, and patenting at founding time, finding that the VC-backed firms have slightly more patents than the control group on average (about one half a patent difference).