2021 ACS showing steep decline in number of workers

[Chris_B]

The reason is that weights are specific to the sample and you are changing the sample by restricting to 1 year. A helpful way to think about it might be: if you take 1 year of the 5 year ACS, you are taking the sample down to 1/5th of the total-- your weights will then add-up to 1/5th of the total that you want, makes sense from that perspective! For another good example to understand this issue (from the flip-side of the same coin as yours; adding samples together) there’s a similar post using the “Form 1” and “Form 2” in the 1970 ACS. It is a good idea to pool the 1970 form 1 metro sample and 1970 form 2 metro sample together