Statistical analysis
Statistical analysis was performed using R v 3.5.2. Descriptive statistics were performed using percentage (%) for categorical variables and using median and interquartile range [IQR] for continuous variables since the LOS was right-skewed (non-normal). Consequently, univariate analysis was performed using Mann-Whitney and Kruskal-Wallis test for non-normal dependent variables (e.g. LOS) when the independent variable had two and three levels, respectively. Chi-square test of independence was used to assess the association between anaemia and the need for transfusion.
Negative binomial regression (NBR) was used to assess the association between anaemia and LOS. Age, gender, and site of surgery (knee vs. hip) were included as covariates to the model as a separate interest.