We have done a simple pilot study where we measure the number of bacteria on the tip of a bronchoscope two times on the same 20 subjects. Half of these subjects have received an intervention to reduce the number of bacteria. So in a long dataset with 40 observations I have the following variables
Idnr - subject ID
meas - binary variable indicating first (=1) or second (=2) measurement
flush - binary variable whether the subject have received (=1) or not (=0) the intervention
bal - measurement of bacterial load
What I would like to do, is to test whether the difference between measurement 1 and measurement 2 is depending on whether they have received the intervention. I've tried various ANOVA syntaxes, but my limited knowledge won't quite get me there.
Probably this reveals my incompetence, but nevertheless I hope for an answer that is understandable for a non-statisician.
Rune Nielsen, MD, PhD, postdoctoral fellow Institute of Medicine Department of Thoracic Medicine Haukeland University Hospital N-5021 Bergen Norway