The first element, -supply at the time of production-, leads to first peculiarities of services. At the time of making the contract of purchase the customer cannot test or even examine the quality of the service. He can only estimate the potential qualities of the service provider and hope that a certain quality will be reached. On the other side, the service provider can hardly give a promise that a certain quality will be reached as he often does not know the exact condition of the external factor, i.e. the process carrier. In our case the ophthalmologist does not know for certain, how the eye will heal after surgery. The promise that a certain quality will be reached becomes even more difficult, if the service applied depends on human performance. For once there are intra-individual changes, the individual performance will depend on daily conditions (daily output, sympathy, temper). Secondly, the individual performance will be different due to experience, skill, and knowledge.

The second element, -immateriality-, will make unbiased quality measurement difficult, and the reputation of quality measurements even harder. Immateriality means missing the availability of the performance's storage.

The third element, -integration of the external factor-, most profoundly effects quality aspects of service. The quality of the performance will depend on the external factor:

1. The quality is not under total control of the service provider. It is unlikely that the external factors will be identical. For instance, different shapes of the external factors will influence the outcome.

2. That outcome is connected with the external factor, implies that quality can not be purified by sorting out defects after the service process. A replacement of unsuccessful service is also impossible. Only the offer of a possible improvement or the reduction of price is possible. This feature is of upper importance when service is applied on the customer himself.

3. Moreover, if service is applied directly on the customer, the process of integration will be of interactivity and the formal outcome will depend on this interactivity.

The interactivity also implies that the performance is not only a production process, it is also a process of consuming and an experience by the customer. Many aspects of quality will be transitory and pass away, they cannot be reconstructed. One could suggest that medical care is not a night-club, that is to say, that actively consuming the service is not the aim of medical care. However, it is an important feature in medical care, because as patients don't have the knowledge to judge the quality, the experience during their stay makes a strong impression, Hopefully to the benefit of the institution.

4.3 Summary
The quality of service is a very complex phenomenon. It will be determined by the customer or its object, the external factors, and by the service provider itself. The more persons directly involved in the production process, the more difficult it will be to interpret the quality reached. Medical care represents this most difficult situation, as customer and service provider are human beings. The quality depends on the potentials and interactivity of the two, the patient and the physicians. The attained quality can not be isolated from the process carrier, in our case the patient. Therefore the go trough rate is 100 % by defintion. Quality in medical care has always been of a very subjective character, the patient will, whether he wants to or not, influence the quality and feel quality subjectively. The following figure will summerise the nature of service and its implication for quality as discussed so far in this chapter.
 
Figure 8: The Nature of Service