Final answer:
An extra wage compensates workers for various reasons such as improving productivity and motivation according to efficiency wage theory, which posits that higher than market wages can reduce employer costs in the long term.
Step-by-step explanation:
An extra wage can compensate workers for various reasons beyond their basic salary, including undesirable working conditions, incentive for performance, or overtime work. According to the efficiency wage theory, employers may decide to pay an efficiency wage that goes above the market rate to increase worker productivity and reduce turnover costs. Workers receiving higher wages tend to stay motivated and more likely to remain with the company, which in turn minimizes the employer's costs associated with training and hiring new staff.
While an extra wage could represent different forms of compensation such as performance bonuses or overtime pay, the theory particularly highlights the role of wages in worker productivity and motivation, rather than being directly tied to specific tasks or performance milestones.