Morbidity Rate: MR(i): As shown in the upper part of Figure 1, the population is divided into two groups – – healthy (HP) and sick (TS). Sick defines persons with some disease, regardless of the treatment. The person himself may not know that he is ill: these people are included with the TS at this stage. There are also some people who consider themselves sick but, from the medical point of view, are actually not sick at all. They visit physicians, only to be examined and told that they are in fact healthy. But, since they are nonetheless consuming medical resources, they are classified with the „total sick“ group.
Since this is a dynamic process, a rate can be assumed between these two amounts, namely, the number of persons transferred from the healthy stage to the sick stage in a unit time. This rate is defined as the morbidity rate (MR).
Since the number of total sick is not known, it is usually difficult to estimate the morbidity rate, except for some special circumstances. This will be discussed later.
Recovery Rate: RECOV(i): Persons who get illnesses may recover – – in some cases after medical treatment and in others spontaneously. This summary rate may be defined as the recovery rate (RECOV).
Death Rate: DR(i): Persons who get illnesses may die even after medical treatment. This rate is defined as the death rate of patients (DR). Note that this rate is different from the ordinary death rate in health statistics (the number of persons who die per unit of time, divided by the total population): when there are more healthy persons, the ordinary death rate decreases. Accordingly, the ordinary death rate represents more the number of sick persons or the prevalence rate, whereas the death rate of patients reflects, in some part, the level of medical care. This will be discussed in the next sections.