define the difference between retention and turnover
Turnover is the percentage of employees who leave voluntarily in a given time period. New job offers, retirement, relocation and job dissatisfaction often trigger voluntary separations. Terminations, furloughs and layoffs are examples of involuntary separations and aren't reflected in turnover rates.
Retention is the percentage of people who were on staff and remained there from the start to the end of a time period, say, a year's first quarter. Employers can track the workers in this group and extract such information as occupation, rank or age.