Hello, I have a question with "on which."<br/><br/>" the control group comprised 295 infants on which retrospective chart data were available over an earlier three-year period."<br/><br/>what exactly does "on which" modify in this sentence?<br/><br/>does this sentence mean "the control group is comprised of 295 infants, and their past data is only available for the earlier three-year period"?<br/><br/>if you could change this sentence into more informal(easily understandable) way, i would appreciate it.<br/><br/>Thank you!