I find that the sample size for 2018 IPUMS CPS Outgoing rotation group (ORG) data is about 10 percent of the 2018 NBER CPS Outgoing rotation group data. Is there an explanation to why the sample sizes are different?

If, however, the mismatch is because of how the IPUMS CPS ORG data is downloaded, I have used the following criteria – Downloaded 2018 ASEC sample with ORG variables, and used the following conditions to isolate the ORG sample – Age = 15+; EMPSTAT = 10-12; CLASSWKR= 20-28; MISH= 4 or 8. Does this work?

Thanks for your help!