Table 2.

Describing variability of functions in FRAM. Each type of function can be affected by Endogenous (internal) and Exogenous (external) variability²⁶

Type of function	Description	Endogenous variability	Exogenous variability
Human	Carried out by individuals or small groups. Variability is often of high frequency and amplitude. High amplitude can lead to positive and negative outcomes.	Physiological and psychological factors such as fatigue and stress. These may be induced by workload or different working practices.	Social factors such as peer pressure, social norms and expectations. Other factors such as public expectation, and standards. Commercial and political considerations can affect human function.
Technological	Equipment and devices. Technological functions are assumed to be stable and reliable most of the time but it is appreciated they can be variable.	Inner workings are complicated and there is inevitable component degradation.	Inappropriate maintenance and inappropriate working conditions.
Organisational	Organisational functions are performed by groups with defined work activities. Organisational variability is thought to be of low frequency but high amplitude when it does happen. This is thought to be that that organisational functions are mostly systemic.	Organisational functions are affected by reasons such as communication, authority gradient and culture.	Environmental factors: regulation, public requirements, financial pressure, weather, politics.