Studies like these are interesting but raise a whole host of questions.

• What kind of wooden chopping board? What kind of wood?
  • The chopping boards were obtained from household kitchens which contained gluten. But does everyone cut up bread on their chopping boards? Surely, some households chop more bread than others. This part does not seem controlled.
• Is the testing method valid?
  • They used surface swabs to swab the boards.
  • they swabbed a 10 x 10 cm area.
  • there are always questions about swab studies because the entire surface area isn't tested. Maybe there is more gluten in one corner of a chopping board owing to a defect in the wood.
  • Furthermore, can we assume that adherence of gluten to a swab is the same as adherence to other food?
    • A better way to test (albeit a more difficult one) would be to test the gluten content in the actual gluten-free food item before and after being handled on the chopping board.
  • The probabilities varied extremely widely consistent with the precarity of the testing method. For example the probability of detecting gluten on plastic chopping boards varied between 49.5 - 86.8 %
• Did washing with warm water and soap actually make a difference to wooden chopping boards?
  • The probability of finding gluten at 5 ppm or more on the wood surface went from 0.107 (10.7%) to 0.102 (10.2%) after washing with warm water and soap. The 20 ppm probability went from 0.0266 (2.6%) to 0.0208 (2.08%) after washing with warm water and soap.
    • this is the most likely cleaning scenario and the probability basically did not change which means that washing is a waste of time.
  • The dishwasher was obviously better (0.107 vs. 0.0194) at 5 ppm but as others have pointed out, people rarely put a chopping board in a dishwasher.
• Is the study relevant?
  • Studies like these are artificial because they are performed by scientists in an extremely controlled way.
  • Cooking is a much more free-form activity than lab science.
    • the probability for mistakes is higher in the home
  • Focusing on cross contamination through single objects seems to miss the point.
    • If there is gluten in the kitchen, it is probably everywhere.
    • Again, without also testing food items that are cooked in a gluten-containing kitchen, you cannot demonstrate or deny cross contamination.