I am working on a project using secondary data from the Millennium Cohort Study. For my analysis, I need to include children with different-aged siblings but exclude twins and siblings. Each family in the study has a unique ID number, which appears multiple times when participants are twins or triplets.

How do I select cases where the ID number only appears once in the dataset or remove cases where the ID number appears more than once? I am familiar with the Select Cases function, but I'm unsure how to handle this issue.

This is not removing duplicates, as this option would only remove one of the twins or triplets, not the entire set.

Any assistance would be greatly appreciated!