What are the accident rates for kit built aircraft vs. normal aircraft of the same model?
The Australian Transport Safety Bureau did a report titled:

Amateur-built aircraft Part 2: Analysis of accidents involving VH-registered non-factory-built aeroplanes 1988-2010 

This report specifically covers this and found that the accident rate was three times higher in kit built -vs- similar factory build aircraft:


  What did this report do  
  
  The ATSB investigated the safety history of amateur-built aircraft in
  Australia through analysis of accident data held in the ATSB’s
  occurrence database from 1988 to 2010. Comparisons were made between
  accidents involving amateur-built aircraft and those involving similar
  factory-built aircraft to help identify whether the rate and types of
  accidents differed between these two groups of aircraft.
  
  What the ATSB found
  
  Amateur-built aircraft had an accident rate three times higher than
  comparable factory-built certified aircraft conducting similar flight
  operations between 1988 and 2010. The fatal and serious injury
  accident rate was over five times higher in amateur-built aircraft, in
  particular due to relatively more serious injury accidents. The pilots
  of amateur-built aircraft involved in accidents were significantly
  more experienced overall than factory-built aircraft accident pilots.
  However, they were significantly less experienced on the aircraft type
  that they were flying at the time of the accident.
  
  Over half of the accidents were precipitated by mechanical events,
  which were mainly complete or partial engine failures. Following the
  amateur-built phase one test period, mechanical failures were still
  significantly more common when compared with factory-built aircraft. A
  quarter of accidents were from loss of aircraft control. Structural
  failures were not common precursors in amateur-built aircraft.
  Collision with terrain and forced landing accidents were more frequent
  in amateur-built aircraft. Collisions with terrain, hard landings, and
  runway excursions were more likely to result in a serious injury from
  an amateur-built aircraft accident than for factory-built accidents.


On the other hand, the EAA says that homebuilt aircraft have an accident rate of less than 1% higher than the general aviation fleet in their FAQ, but this didn't compare homebuilt to factory built in similar models:


  How Safe Are Amateur-Built/Homebuilt Aircraft?
  
  Studies by FAA and the National Transportation Safety Board (NTSB)
  show that Amateur-Built/Homebuilt aircraft have an accident rate less
  than one percentage point higher than the general aviation fleet. In
  fact, the accident rate for Amateur-Built/homebuilt aircraft is
  dropping. The total number of registered homebuilt aircraft is
  increasing by about 1,000 per year, while the total number of
  accidents has stayed virtually the same. Another good barometer of
  safety is insurance rates. Companies that insure both homebuilts and
  production aircraft charge about the same rates for owners of either
  type of airplane. That indicates a similar level of risk.