ABSTRACT
This chapter discusses common research scenarios and statistical issues that will come up. For blood loss, how will it be measured or estimated? Is there an idea how much blood loss is truly excessive? We review the Charlson comorbidity index and the rationale for updating it. We discuss the minimal clinically important difference and why that is a more complicated concept than it would immediately seem. Lastly, we review the body mass index and problems inherent in using a predictor based on a ratio.
