This procedure is confidential testing. Confidential testing is a method of data collection where the participant's identity is known to the researcher, but is kept confidential and not disclosed to others. In this case, the researchers assign each participant a code, so they can link the results to a specific participant but do not disclose their identity to others. In contrast, anonymous testing is when the participant's identity is not known to the researcher or anyone else, so there is no way to link the results to a specific participant.