To get a percentage, you need to do more than just sum. I would create a formula that looks something like this (assumes that you have a group on the date that's set to view monthly):
Sum({table.COLD_IN_TIME_FRAME}, {table.DateField}, "monthly") % Count({table.BABY_MRN}, {table.DateField}, "monthly")
This will display the values and
might work in the chart. Also, the "%" operator will automatically give you a percentage that automatically multiplies the result by 100 instead of you having to explicitly do the multiplication in the formula.
-Dell