The fixed overhead volume variance can easily be explained as being caused by the production level—that is, by making more or fewer units than budgeted. Why is the same not true of the direct...

The fixed overhead volume variance can easily be explained as being caused by the production level—that is, by making more or fewer units than budgeted. Why is the same not true of the direct materials quantity variance, the direct labor efficiency variance, and the variable overhead efficiency variance?