No, assigning participants to a group based on their preferences in an open-label manner is not considered allocation sequence concealment. In an open-label study, the researchers and often the participants are aware of the treatment assignments, which means there is no concealment of the allocation sequence. This lack of concealment can introduce bias and compromise the validity of the study because participants and researchers may consciously or subconsciously influence the assignment process, potentially leading to biased results.

Allocation concealment is typically achieved through methods like using sealed, opaque envelopes, central randomization systems, or automated allocation procedures to ensure that neither the researchers nor the participants can predict or influence the group to which a participant will be assigned until the actual allocation occurs. This helps maintain the integrity and validity of the research findings.