(a) Except as provided in (b) of this section, compensation or benefits are payable under this chapter for disability or death or the need for medical treatment of an employee if the disability or death of the employee or the employee's need for medical treatment arose out of and in the course of the employment. To establish a presumption under AS 23.30.120(a)(1) that the disability or death or the need for medical treatment arose out of and in the course of the employment, the employee must establish a causal link between the employment and the disability or death or the need for medical treatment. A presumption may be rebutted by a demonstration of substantial evidence that the death or disability or the need for medical treatment did not arise out of and in the course of the employment. When determining whether or not the death or disability or need for medical treatment arose out of and in the course of the employment, the board must evaluate the relative contribution of different causes of the disability or death or the need for medical treatment. Compensation or benefits under this chapter are payable for the disability or death or the need for medical treatment if, in relation to other causes, the employment is the substantial cause of the disability or death or need for medical treatment.

(b) Compensation and benefits under this chapter are not payable for mental injury caused by mental stress, unless it is established that (1) the work stress was extraordinary and unusual in comparison to pressures and tensions experienced by individuals in a comparable work environment; and (2) the work stress was the predominant cause of the mental injury. The amount of work stress shall be measured by actual events. A mental injury is not considered to arise out of and in the course of employment if it results from a disciplinary action, work evaluation, job transfer, layoff, demotion, termination, or similar action taken in good faith by the employer.