Labor usage is controllable at the supervisor’s level. Even so, unfavorable labor variances may be due to defective materials, defective tools, mechanical failures, or other circumstances beyond the supervisor’s immediate control. In addition, the wage rates are often determined in management-union negations. However, the wage rate variance is frequently controllable at the supervisor’s level. To illustrate, a supervisor may cause a wage rate variance by using workers with higher wage rates than the rate specified for a particular operation. In any event, a supervisor should comment on each significant variance - about its cause and how it will be corrected. Consistent reporting of wage rate variances (favorable or unfavorable) calls into question the validity of the standards being used