The cause of these variations is rarely unique and more often composed, in varying proportions, of different factors from the triad formed by the patient, the health care provider and their environment. These causes can also be divided up into supply- or demand-related causal factors.
In general, although the causes identified sometimes may indicate a non-optimal use of resources, they cannot always be described as unjustified and the existence of variations is therefore not automatically to be accused of inefficiency in the health care system.
The causes of variations are in any case to be considered on a case-by-case basis depending on the theme analysed and its context. If we consider again the categorization of these factors according to supply and demand, here are in a very brief way the main categories of causes that can be found, as identified by the KCE , with the exception of possible unknown factors in coding by health care providers:
- Demand-related causes :
- Epidemiology of the disease
- Socio-economic variables
- Patient's choice
- Supply-related causes :
- Medical density
- Access to health care
- Characteristics and practice style of the health care provider
 J. Jacques, D. Gillain, F. Fecher, S. Van De Sande, F. Vrijens, D. Ramaekers, N. Swartenbroekx and P. Gillet (2006). Étude des disparités de la chirurgie élective en Belgique Brussels : Belgian Health Care Knowledge Centre (KCE) KCE Reports vol.42B.