Compensation costs are defined as the sum of wage and salary accruals and supplements to wages and salaries. Wage and salary accruals consist of the monetary remuneration of employees, including the compensation of corporate officers; commissions, tips, and bonuses; voluntary employee contributions to certain deferred compensation plans, such as 401(k) plans; employee gains from exercising nonqualified stock options; and receipts in kind that represent income. Supplements to wages and salaries consist of employer contributions for social insurance and employer payments (including payments in kind) to private pension and profit-sharing plans, group health and life insurance plans, privately administered workers' compensation plans. For employees (wage and salary workers), hourly compensation is measured relative to hours at work and includes payments made by employers for time not at work, such as vacation, holiday, and sick pay. Because compensation costs for the business and nonfarm business sectors would otherwise be severely understated, an estimate of the hourly compensation of proprietors of unincorporated businesses is made by assuming that their hourly compensation is equal to that of employees in the same sector.