If you’re among the 1.6 million service members who are eligible to choose between the old or new retirement systems, an advocacy organization wants you to take a survey about why you made the choice.

Service members eligible to opt in to the new Blended Retirement System or stay with the legacy system are active duty members who had fewer than 12 years of service — and reserve-component members in a paid status with fewer than 4,320 retirement points — as of Dec. 31, 2017.

Those with more time in the military automatically stay with the legacy system; those entering on or after Jan. 1, 2018, are automatically enrolled in the BRS.

The deadline for this eligible group to opt in to the new system is Dec. 31, 2018, and the Military Officers Association of America is seeking input from those who have already made the choice. If you’re not eligible to make the decision, you won’t be able to take the survey. If you haven’t yet made a decision, it doesn’t give you the option of noting that.

The anonymous, short survey will be available online through mid-December.

It includes 21 questions, and takes about 15 to 20 minutes to complete. The questions are all multiple choice, with eight questions related to demographics such as branch of service and age. It includes questions about past and present career plans, sources that had the most impact on the choice, the Thrift Savings Plan, and more.

MOAA officials want to know what factors played into service members’ decisions, said Mike Barron, a retired Army colonel who is MOAA’s director of government relations.

“We wanted to get a good feel in this opt-in year for why people made the decisions they made,” he said. “It’s all a personal choice, but a lot of information goes into that very personal decision of whether they should opt in to the new retirement system or stay with what they have.”

Some of those factors include the spouse, and whether they think they’ll be able to stay in the military until retirement.

MOAA also wants to know whether you think the information provided by the Defense Department and the services has been useful to you in making the decision.

Barron said the information from the survey will be shared with Defense Department officials and other advocacy organizations.

The Blended Retirement System is a combination of the legacy retirement system and some new features. Like the legacy system, it provides monthly retired pay after at least 20 years of service — but the monthly check is about 20 percent less than what it would have been under the legacy system.

However, unlike the legacy system, those in the BRS receive a matching contribution to their Thrift Savings Plan from the Defense Department. DoD automatically matches 1 percent, then as much as 5 percent if the service member contributes at least 5 percent. So, under BRS, if a service member leaves before retirement, they take something with them — that DoD matching contribution.

At the 12-year point, BRS members can receive continuation pay in return for a commitment to serve an additional four years. And instead of waiting for the monthly check, retirees under BRS can choose a partial lump-sum payout.