Most Analysis and Statistic routines work DataSet-based.
This means Events and codes are calculated and compared only per DataSet. Most results show the data split per DataSets, but other structures are also available.
Many statistics are available directly under Analysis - Evaluation - Statistics 
, but not all. Some are only available from within the Timeline Chart.
For all statistic Routines, it is possible to limit the results to a specific number of Codes and/or DataSets.
That is why each routine first asks you to select the DataSets to which the routine should be applied followed by a dialog to select only the Codes you are currently interested in.
IMPORTANT: To get an overview of all your observations at once, use one of the available merge routines to create one big compilation file.
You might need multiple versions of the same data to answer all your research questions.
For this INTERACT offers a range of restructuring routines.