Final answer:
Among the given options, 'Labor hoarding' is typically not considered a factor contributing to real-wage rigidity in the Keynesian model, while the other options are valid explanations for why wages do not fall easily even during economic downturns.
Step-by-step explanation:
The question addresses real-wage rigidity in the Keynesian model by considering which factors are not typically used to explain why wages do not tend to decrease, even in poor economic conditions. Among the options presented, A) Turnover costs, B) Legal and institutional factors, C) The efficiency-wage model, and D) Labor hoarding, all are indeed reasons often given for real-wage rigidity except for Labor hoarding. When businesses keep more workers on the payroll than necessary to avoid costs associated with firing and later rehiring or retraining, that is typically referred to as labor hoarding, rather than a factor that causes wage rigidity.
Economists have found that sticky wages in the labor market may contribute to short-run or long-run unemployment. The reasons wages remain sticky can include turnover costs (the costs associated with replacing workers), legal and institutional factors (such as minimum wage laws or employment contracts), and the efficiency-wage theory (where employers pay above-equilibrium wages to increase productivity and discourage shirking).