On page 322 we could find entry employees (EE) and interns (I) from year 2011 to 2017. Based on other metrics we had total employees for period t (TE_t) and period t-1 (TE_t-1). Turnover rate (TR) is the rate between separated employees (SE) and average employees (AE = (TE_t + TE_t-1)/2). Then, we estimated this metric as TR = SE/AE = (TE_t-1 + EE + I - TE_t)/AE = (TE_t-1 + EE + I - TE_t)/((TE_t + TE_t-1)/2)