"Pref" stands for preferred and can be set to either yes or no in the Proposal census. Setting the "Pref" status to yes for a participants marks them as part of the preferred group. Setting their status to no, excludes them from the preferred group. This status will be used for reporting only, to illustrate to the plan sponsor how the plan will benefit the preferred group as compared to the remainder of the participants in the plan. This can be beneficial in helping the plan sponsor identify which proposal scenario will benefit the preferred group the most.
Please note that this status is not used in testing in any way and any scenario that a plan sponsor selects will need to pass all required testing to verify that the plan is not discriminatory.