The expert statistical analysis alluded to is simply the framework for causal inference. Had Letby not been on duty for a similar group of patients, would the n

The expert statistical analysis alluded to is simply the framework for causal inference. Had Letby not been on duty for a similar group of patients, would the number of patients who had died been the same? If the answer is no, then a follow on question regarding whether or not factors associated with Letby could have resulted in the deaths rather than Letby herself. This could be a fellow worker who always worked in tandem with her etc. Finding the appropriate set of data and applying statistical techniques for this is not trivial hence the expert mention.