The official Challenge rules
[30] stipulate that the participant must agree, in writing, to the conditions and criteria of their test. Claims that cannot be tested experimentally are not eligible for the Challenge. To ensure that the experimental conditions themselves do not negatively affect a claimant's ability to perform, non-blinded preliminary control tests are often performed. For example, the JREF has
dowsers perform a control test, in which the dowser attempts to locate the target substance or object using their dowsing ability, even though the target's location has been revealed to the applicant. Failure to display a 100% success rate in the open test will cause their immediate disqualification. However, claimants are usually able to perform successfully during the open test, confirming that experimental conditions are adequate. According to the JREF, despite success in these open tests, no claimants have yet been able to successfully demonstrate evidence of their claims while blinded under otherwise identical conditions. Some participants have stated afterwards that the threat of disqualification is the main factor in their apparent success in the open test. Randi has said that few unsuccessful applicants ever seriously consider that their failure to perform might be due to the nonexistence of the power they believe they possess.
[31]
