I am working with NIS data which are basically a 20% sample of all in-hospital admissions in the US every year. I have small group of cases that carry diagnosis "X" in their record and overall the only consist of 0.1% of the total n.
I would like to compare that group with cases "without diagnosis X". As you realize, with a total n= 6 million, the "diagnosis X" group is way too small for comparing associated characteristics against the "without diagnosis X" group (chi-square and t-tests, even regression)
Is there a way to control for this "overpowering" of the control group?
I use SPSS 23