What are the different types of Probability?

In contemporary writings two main theories of probability are found to be discussed. They are the frequency theory of probability and the reasonableness of belief theory of probability.

The frequency theory of probability emphasises on statistical evidence. In some sciences like meterology, genetics, biology etc. we mostly rely on statistical evidence. This theory records the frequency with which members of a class exhibit a specified attribute.

On the basis of this statistics certain probable assumptions can be made. Suppose 1000 children are randomly selected for case study. It was found that 95% of the children suffered from diahrrhoea when they were below the age of one year.

Out of them 2% of children succumbed to death when they suffered from diarrhoea. Again another study showed that out of 1000 tribal children 80 per cent of them had suffered from diarrhoea when they were below the age of one year.

Twenty five per cent of the tribal children succumbed to death in diahrrhoea. So the probability of survival of the tribal children suffering from diarrhoea is less than the rate of survival of other non-tribal children.

Thus the frequency theory takes account of probability on the basis of statistical investigation. Here the attribution of probability is measured on the basis of relative frequency with which the members of a class show some characteristic feature.

The reasonableness of belief thory of probability holds that between two positions one is worthy of acceptance if it is more reasonable to accept it on the basis of available evidence. Out of two statements compared with a common body of evidences one may be more rational than the other.

The theory of evolution is more probable a doctrine than the theory of creation. For the former is more rational and reasonable to be believed. Similarly when modern physics and astronomy had riot developed like today and the geocentric theory was the accepted hypothesis the heliocentric theory made a break though in 16th century.

The heliocentric theory was found to be more reasonable than the geo-centric one because it could explain more facts than the later.

Sometimes when the numerical value.of probability is not known or the evidences at hand are too inadequate we are guided by sheer guess or vague impressions. The evidence at hand may be very complex and thereby baffling.

That reduces the probability of a claim. At times the statistical enumerations can make extravagant claims. Even unscrupulous people deliberately give false figures with a purpose. These negative points reduce probability to chance or chance coincidence. Probability can be linked with chance though there is important difference between them.

When the occurrence of a phenomenon is quite unexpected we call it a matter of chance. Similarly if two events coincide or occur together we treat this coincidence or succession as also due to sheer chance, if no lav/, causal relation or even probability is traced in the occurrence of the events.

That means when there is no ground to infer a phenomenon or there is no uniformity in its occurrence we treat it as a chance-occurrence. But probability is different from chance.

The frequency.in the occurrence of events, statistical enumerations or reasonableness of a phenomenon on the basis of our cumulative experience helps to ascertain the probability of some circumstance. That is, the probability of a generalization or inductive inference is not by sheer chance. There is evidential support or source hehind them. Either in analogical induction, induction per simple enumeration or legitimate hypothesis there is probability. So while probability is evidence-supporting, a chance is not.