# longitudinal identifiers after 2000 **URL:** \ **Category:** CPS\ **Created:** [May 31, 2014, 11:59pm UTC](https://forum.ipums.org/t/longitudinal-identifiers-after-2000/541 "2014-05-31T23:59:00Z")\ **Posts on this page:** 1\ **Showing post:** 2
**Author:** ![grover](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.ipums.org/grover/32/5_2.png) [@grover](https://forum.ipums.org/u/grover)\ **Post date:** [June 2, 2014, 5:22pm UTC](https://forum.ipums.org/t/longitudinal-identifiers-after-2000/541/2 "2014-06-02T17:22:00Z")
It is not possible to track people across time using the ACS. Since the ACS was not designed to track households across time the way the CPS was, there are no identifiers created for this purpose. Furthermore, once a household is included in an ACS sample it is not allowed to be sampled again for five years. The methods NBER uses for linking March Samples across years can be applied to beyond 1998 since the survey has not undergone a major restructuring since 1994. See [this answer](https://forum.ipums.org/t/how-do-you-link-join-a-tobacco-supplement-from-jan-to-a-march-sample-with-income-data/446/1) for more information on using this method with IPUMS-CPS data. I hope this helps. --- _[View the full topic](https://forum.ipums.org/t/longitudinal-identifiers-after-2000/541)._